user2467: I want to know whether chess is a game of skill or game of chance, and how much is the degree of skill or chance in terms of percentage.
Edit (21 Feb 2014):
Please make sure that your answer includes credible references. To be sure that chess is a game of skill (or chance?).

user2474: Chess is definitely a game of skill and not by chance. One of the greatest chess players ever was the American Robert James "Bobby" Fischer. He acquired the skill by training everyday. He brought a chess board with him wherever he went, even while taking a bath.
It will take you more or less 10 years of real training to become a Grand Master or, at most, a world champion.
I am just barely 2200 FIDE rated but I can say skill is 95% and the rest is where the luck goes.

user1522: In theory, chess is 100% game of skill. But since chess is unsolved in practice, is it purely a game of skill?
As of today, if a human/computer analyse to some depth D and result in N board positions with same evaluation E, then the final choice could be purely random. 
Therefore until chess is solved, with limited computing power, there is a small component of chance.
Edit:
Consider 2 computers playing against each other. Lets say, in theory, we know that 1.e4 wins, 1.d4 loses. But the computers have limited power and evaluate both 1.e4 and 1.d4 as same. The computer randomly breaks the tie - winning or losing by chance.
Edit 2:
How much of it is chance?
IMO the chance component depends on the evaluation depth. For 2 computers that can analyse only upto a depth of 1 - the chance component is high.
Edit 3:
Definition of chance:
An external source of randomness which is not known to either playing agents. 2 computers playing each other can produce different result.

user2499: I'm pretty sure that by formal definition, chess is a game of 100% skill and 0% luck. Why? There is no "outside element of randomness" that could influence the outcome of a match but cannot be directly controlled by at least one of the players. 
In other games, the order of cards and the outcome of the roll of a die cannot be influenced by players... at least not if they play by the rules and do not use some mechanism of cheating :)
The inherent "human factor" is not considered "chance". I.e. if player B makes a mistake that lets player A win, we don't say player A was lucky, we say he played a better game because B made a mistake and A didn't. Of course players can introduce an element of chance/randomness by making random moves. If a position is too complex for a player to understand, he could mentally or actually flip a coin to decide which move to make. Or he could pick the best move for completely wrong reasons. This sort of "chance" is part of every game, so if you want, consider it 1-5% chance. More for beginners, less for skilled people because skilled people will not need this type of "guessing".
Another thing to consider: A good player will not lose a single game against a weak player. I don't think the same will be true for poker or other games involving chance so this also shows that it's a game of high skill and little chance... 

user3848: No, chess requires 100% skill, that's why bookmakers may offer poker games, dominos etc., but absolutely not chess because a good player will constantly win.

user1811: I would submit that there is an element of luck in chess. For eg., imagine a game between two players of roughly equal ability. Suppose the position becomes a very open tactical position with possibilities for both sides. In such a situation a lot of tactics are possible. As human beings, we may not be able to calculate all the variations in such a position. So in such a situation, we would normally choose a particular tactic based on gut feeling. It may well turn out that the tactic chosen is the best one which may result in a winning advantage. However, given the open nature of the position, it may also turn out that the tactic chosen is not a great one and that the opponent finds a good refutation for that particular tactic. So there appears to be an element of luck in deciding which tactic to choose in a position which offers many possibilities.

user478: As chess isn't completly solved, nobody can guarantee that 1.a4 doesn't force a win. However people don't play perfectly (there is room for error), so people will try to use familiar paths to increase his chances of winning. With trial and error they know what is more likely to work and than not.
A cat (by luck) can beat us in chess by slamming his paws (very unlikely, but it remains possible). But why is a GrandMaster more likely to win than a cat?:

Grand Masters are very skilled in picking the moves that have more
  chances of winning.

The question "is chess a game of skill or chance?" can be reworded to "will a cat win more than about 50% of the time in chess or not?". And then the answer is obviously clear, chess is a game of skill.
But, is there some luck involved? Yes, a cat can beat us by chance.
To how much extent is chance involved? Here is the hard question, as long as players don't calculate 100% of the possible replays and future moves, they are trying to guess which move will perform best, they can rarely calculate everything (only possible in the late game or forced moves by check on the early/mid game). My guess would be that they can't calculate everything 98% of the time, maybe 95% without time limits like correspondence chess.

user2471: White always starts with a slight advantage by having the first move. So if your colour is decided by flipping a coin or whatever, then that's an element of chance! 
But it has been accepted that the game itself is 100% skill.

user2497: As a game of chess progresses from one of incomprehensibly vast complexity (with a great many useful moves open to many pieces) to manageable complexity (with fewer useful moves), play transitions from (hopefully) skillful (conscious or subconscious/intuitive) applications of

heuristics, probabilities, and targeted but incomplete analysis (often small differential analysis from remembered/studied games), to
exhaustive analysis of the relevant paths the game may still take (again, often differential analysis from reference games).

The players themselves - and human observers - may not be able to reliably identify this transition, as they'll be prone to feel like they're in stage 2 a little early - while there are still one or more potential plays that could upset their plans.  And a careless move may transition a player back to stage 1.
There's definitely skill involved in both stages: in as much as skill is "the ability to do something well; expertise" (OED) - and many reasonable criteria for "doing [chess] well" are possible, such as say:

one's ability to find "better" or avoid subtly "worse" moves, whether in stage "1" or "2" above, and where
"better" and "worse" are evaluated by the impact those moves have on the outcomes of games they and/or other players have after those moves, all compared to others in the chess-playing community.

(I phrase it in terms of individual moves and not "wins"/"loses averted" because in any activity someone may have skill but not consistency; they may not be a great competitor e.g. if they're feeble of concentration, flustered by pressure, unable or even uninterested in manifesting their ability consistently in competitive settings; they might just like analysing complex end games for example, but be very good at it...).
In stage 1, there's also an element of luck: there's at least the potential for:

some reasonable-seeming move to turn out poorly (which would be unusual and therefore reasonably deemed "unlucky" if the heuristics and partial reasoning were overwhelmingly sound and skillfully applied - i.e. of a high standard compared to the chess community overall), or 
a great opportunity that wasn't deliberately set up to become available, or
a relatively careless move to have consequences that weren't foreseen, which might work out very well or very poorly.

But, if one player has a lot more skill than the other player, the frequency and severity of significantly "unlucky" moves they might make, or "lucky" moves their opponent might make that they hadn't foreseen and protected against, decreases, until it becomes astronomically unlikely for enough consecutive "(un)lucky events" to have more bearing on the outcome of the game than the skill differential does.
On the other hand, the closer the skill level the more likely that "luck" will be the deciding factor.  Here, "luck" might be occasioned by conscious awareness that a choice between moves is being made arbitrarily, or it could be an intuition/hunch to choose between moves that in this case isn't actually usefully informed by any experience or subconscious analysis.  There's even a degree of luck in whether a player making an arbitrary choice between what might in some absolute sense be equally good moves happens to choose a move leading to a situation their opponent is more or less skillful at handling (e.g. because their experience and study is more relevant to one position than another).
You could compare this tide-of-skill versus spontaneous-fluke factor to say tennis: a lucky outcome could see me win a point against Roger Federer - perhaps by playing a very low percentage but skillful shot that happens to work out that one time, or even by having a shot hit the net-cord and drop over, come off my racquet frame at an unlikely but advantageous angle, or bounce strangely for Roger.  But, the chance I'd win an entire game is maybe 0.1% (?), a set would be like winning lotto twice in a row, and a match - well, the universe might end first. (Sane caveats re Roger being mentally/physically fine etc..)
The more a game requires a great many moves to shape and turn the outcome, and the lower the chance for a fluke beyond either players' control, the more predictable the outcomes are, and the more the skill differential ensures the outcome, even if that skill is probabilistic and not deterministic.  Skill is a huge factor in chess, but skill is not a constant for a player - they may be more skillful at handling play from certain positions than others (perhaps they just read a book on a relevant tactic), and occasionally a player of lower average skill might prevail based on some particularly relevant but limited skill (and be deemed lucky that play led to a situation where they could apply it).  In close matches, and perhaps in beginner's matches where more of the movements are made arbitrarily without even a guiding strategy or heuristic used, luck starts to play a significant role.
I think it's interesting to compare this to baseball, I read a book about it years ago that explained how some Wall Street quant types crunched the maths and found that the worst team in the top league had something like half the chance of being the champions that the best team had... i.e. surprisingly little impact on odds came from achievable differences in skill (given the top team had vastly more budget to hire players considered "stars").  For example, while the percentage of swings that made contact varied with batter, the out/1st-base/2nd-base/3rd-base/home outcomes were in similar proportions: you might observe that it took skill to hit the ball more often, but doing so was so difficult and the angle of contact so uncontrollable that what happened when you did basically came down to luck.  Overall, luck could easily swing a game.
Separately, and this may be controversial and I'm not claiming it's true - just reasoning about the implications if it happens to be true:  I saw a study report that when chess grandmasters played good club players, starting at random board positions that would not occur during actual games: the grandmasters lost their main advantage as they didn't have a huge wealth of applicable reference games with which to compare; reduced to actual logical reasoning without any particular advantage - they only had a smidge more than 50/50 chance of a win.  Does that mean chess is less about skill than my above assertions imply?  Is a vast memory of games itself a skill?  I'd say so - it clearly allows you to "do well" in non-random games, and that's all the OED requires.  Further, consider say a language translator - we'd consider the size of their vocabulary to be an aspect of their skill level.

user291: By the commonly accepted definition of "game of skill", chess is 100% a game of skill. It has no random element at all and both players have full information about the game state at all times. Players do say things like "I was lucky that my opponent blundered", but that's not what is generally meant when people talk about "games of chance".

user167: If we remove the component of flawed, human players from the equation and consider just the game of chess itself as it is spelled out by the rules, then chess is purely a game of skill with no room for chance. That is, it is in principle possible for there to be a perfect chess player that plays optimally against every possible move sequence by an opponent, and that perfect player would never falter due to chance or luck. Such perfect players already exist at the level of chess positions with only a handful of pieces: endgame tablebases consist of all the information necessary for perfect play in those positions, and if you play from such a position against an opponent with access to those tablebases, chance can play no role in stopping them from getting their deserved result.
However, the problem of computing a tablebase for the starting position of chess, with its 32 pieces, is far, far from tractable. So while optimal play does exist for all positions in chess, nobody knows for sure what optimal play is for the vast, vast majority of positions. Looked at in that light, when two humans (or even strong chess engines) play a game against one another, something that can reasonably be viewed as chance (for one side at least) can definitely play a role, but for what I have in mind at least, the root cause of any outcome is still skill (or its temporary absence).
Here's an example of what I mean. In the recent Zurich Chess Challenge, Nakamura was playing a fine game against Carlsen, to the point where he had an overwhelming, winning advantage. At that point, it could safely be said that Carlsen "deserved" to lose.
[fen "4r1k1/1p3pPp/6q1/2pPpNP1/p1n1P3/P6Q/7R/K7 w KQkq - 0 1"]
[White "Nakamura, Hikaru"]
[Black "Carlsen, Magnus"]
[Event "Zurich Chess Challenge"]
[Result "0-1"]

1.d6? (1.Qf1!)

But Nakamura made a crucial mistake that let Carlsen off the hook, later followed by further poor play that even allowed Carlsen to win. If someone were to say, "Carlsen was lucky to win that day," I'd say there's truth to that. (Carlsen certainly deserves credit for defending in such a way that Nakamura could still go wrong, but even so, he was fortunate that Nakamura erred as he did.) But the luck from Carlsen's side originated from nothing more than a momentary lack of skill on Nakamura's part. Finding the right move was entirely within Nakamura's power, but he wasn't quite skillful enough to find it in that moment.
As in most human endeavors, there is some element of chance in the competitive results of chess games. But that luck for one side generally comes in the form of what kind of lack of skill one's opponent shows (and when).

2467: <p>I want to know whether chess is a game of skill or game of chance, and how much is the degree of skill or chance in terms of percentage.</p>

<p>Edit (21 Feb 2014):</p>

<p>Please make sure that your answer includes credible references. To be sure that chess is a game of skill (or chance?).</p>
 2474: <p>Chess is definitely a game of skill and not by chance. One of the greatest chess players ever was the American Robert James "Bobby" Fischer. He acquired the skill by training everyday. He brought a chess board with him wherever he went, even while taking a bath.</p>

<p>It will take you more or less 10 years of real training to become a Grand Master or, at most, a world champion.</p>

<p>I am just barely 2200 FIDE rated but I can say skill is 95% and the rest is where the luck goes.</p>
 1522: <p>In theory, chess is 100% game of skill. But since chess is unsolved in practice, is it purely a game of skill?</p>

<p>As of today, if a human/computer analyse to some depth <code>D</code> and result in <code>N</code> board positions with same evaluation <code>E</code>, then the final choice could be purely random. </p>

<p>Therefore until chess is solved, with limited computing power, there is a small component of chance.</p>

<p><strong>Edit:</strong>
Consider 2 computers playing against each other. Lets say, in theory, we know that <code>1.e4</code> wins, <code>1.d4</code> loses. But the computers have limited power and evaluate both <code>1.e4</code> and <code>1.d4</code> as same. The computer <em>randomly</em> breaks the tie - winning or losing by chance.</p>

<p><strong>Edit 2:</strong>
<em>How much of it is chance?</em>
IMO the chance component depends on the evaluation depth. For 2 computers that can analyse only upto a depth of 1 - the chance component is high.</p>

<p><strong>Edit 3:</strong>
<em>Definition of chance:</em>
An external source of randomness which is not known to either playing agents. 2 computers playing each other can produce different result.</p>
 2499: <p>I'm pretty sure that by formal definition, chess is a game of 100% skill and 0% luck. Why? There is no "outside element of randomness" that could influence the outcome of a match but cannot be directly controlled by at least one of the players. </p>

<p>In other games, the order of cards and the outcome of the roll of a die cannot be influenced by players... at least not if they play by the rules and do not use some mechanism of cheating :)</p>

<p>The inherent "human factor" is not considered "chance". I.e. if player B makes a mistake that lets player A win, we don't say player A was lucky, we say he played a better game because B made a mistake and A didn't. Of course players <em>can</em> introduce an element of chance/randomness by making random moves. If a position is too complex for a player to understand, he could mentally or actually flip a coin to decide which move to make. Or he could pick the best move for completely wrong reasons. This sort of "chance" is part of every game, so if you want, consider it 1-5% chance. More for beginners, less for skilled people because skilled people will not need this type of "guessing".</p>

<p>Another thing to consider: A good player will not lose a single game against a weak player. I don't think the same will be true for poker or other games involving chance so this also shows that it's a game of high skill and little chance... </p>
 3848: <p>No, chess requires 100% skill, that's why bookmakers may offer poker games, dominos etc., but absolutely not chess because a good player will constantly win.</p>
 1811: <p>I would submit that there is an element of luck in chess. For eg., imagine a game between two players of roughly equal ability. Suppose the position becomes a very open tactical position with possibilities for both sides. In such a situation a lot of tactics are possible. As human beings, we may not be able to calculate all the variations in such a position. So in such a situation, we would normally choose a particular tactic based on gut feeling. It may well turn out that the tactic chosen is the best one which may result in a winning advantage. However, given the open nature of the position, it may also turn out that the tactic chosen is not a great one and that the opponent finds a good refutation for that particular tactic. So there appears to be an element of luck in deciding which tactic to choose in a position which offers many possibilities.</p>
 478: <p>As chess isn't completly solved, nobody can guarantee that <code>1.a4</code> doesn't force a win. However people don't play perfectly (there is room for error), so people will try to use familiar paths to increase his chances of winning. With trial and error they know what is more likely to work and than not.</p>

<p>A cat (by luck) can beat us in chess by slamming his paws (very unlikely, but it remains possible). But why is a GrandMaster more likely to win than a cat?:</p>

<blockquote>
  <p>Grand Masters are very <strong>skilled</strong> in picking the moves that have more
  <strong>chances</strong> of winning.</p>
</blockquote>

<p>The question "is chess a game of skill or chance?" can be reworded to "will a cat win more than about 50% of the time in chess or not?". And then the answer is obviously clear, chess is a game of <strong>skill</strong>.</p>

<p>But, is there some luck involved? Yes, a cat can beat us by chance.</p>

<p>To how much extent is chance involved? Here is the hard question, as long as players don't calculate 100% of the possible replays and future moves, they are trying to guess which move will perform best, they can rarely calculate <em>everything</em> (only possible in the late game or forced moves by check on the early/mid game). My guess would be that they can't calculate everything 98% of the time, maybe 95% without time limits like correspondence chess.</p>
 2471: <p>White always starts with a slight advantage by having the first move. So if your colour is decided by flipping a coin or whatever, then that's an element of chance! </p>

<p>But it has been accepted that the game itself is 100% skill.</p>
 2497: <p>As a game of chess progresses from one of <em>incomprehensibly</em> vast complexity (with a great many useful moves open to many pieces) to manageable complexity (with fewer useful moves), play transitions from (hopefully) skillful (conscious or subconscious/intuitive) applications of</p>

<ol>
<li><p>heuristics, probabilities, and targeted but incomplete analysis (often small differential analysis from remembered/studied games), to</p></li>
<li><p><em>exhaustive</em> analysis of the <em>relevant</em> paths the game may still take (again, often differential analysis from reference games).</p></li>
</ol>

<p>The players themselves - and human observers - may not be able to reliably identify this transition, as they'll be prone to feel like they're in stage 2 a little early - while there are still one or more potential plays that could upset their plans.  And a careless move may transition a player back to stage 1.</p>

<p>There's definitely skill involved in <em>both</em> stages: in as much as skill is "the ability to do something well; expertise" (OED) - and many reasonable criteria for "doing [chess] well" are possible, such as say:</p>

<ul>
<li><p>one's ability to find "better" or avoid subtly "worse" moves, whether in stage "1" or "2" above, and where</p></li>
<li><p>"better" and "worse" are evaluated by the impact those moves have on the outcomes of games they and/or other players have after those moves, all compared to others in the chess-playing community.</p></li>
</ul>

<p>(I phrase it in terms of individual moves and not "wins"/"loses averted" because in any activity someone may have skill but not consistency; they may not be a great competitor e.g. if they're feeble of concentration, flustered by pressure, unable or even uninterested in manifesting their ability consistently in competitive settings; they might <em>just</em> like analysing complex end games for example, but be very good at it...).</p>

<p>In stage 1, there's <em>also</em> an element of luck: there's at least the potential for:</p>

<ul>
<li><p>some reasonable-seeming move to turn out poorly (which would be unusual and therefore reasonably deemed "unlucky" if the heuristics and partial reasoning were overwhelmingly sound and skillfully applied - i.e. of a high standard compared to the chess community overall), or </p></li>
<li><p>a great opportunity that wasn't deliberately set up to become available, or</p></li>
<li><p>a relatively careless move to have consequences that weren't foreseen, which might work out very well or very poorly.</p></li>
</ul>

<p>But, if one player has a lot more skill than the other player, the frequency and severity of <em>significantly</em> "unlucky" moves they might make, or "lucky" moves their opponent might make that they hadn't foreseen and protected against, decreases, until it becomes astronomically unlikely for enough consecutive "(un)lucky events" to have more bearing on the outcome of the game than the skill differential does.</p>

<p>On the other hand, the closer the skill level the more likely that "luck" will be the deciding factor.  Here, "luck" might be occasioned by conscious awareness that a choice between moves is being made arbitrarily, or it could be an intuition/hunch to choose between moves that in this case isn't actually usefully informed by any experience or subconscious analysis.  There's even a degree of luck in whether a player making an arbitrary choice between what might in some absolute sense be equally good moves happens to choose a move leading to a situation their opponent is more or less skillful at handling (e.g. because their experience and study is more relevant to one position than another).</p>

<p>You could compare this tide-of-skill versus spontaneous-fluke factor to say tennis: a lucky outcome could see me win a point against Roger Federer - perhaps by playing a very low percentage but skillful shot that happens to work out that one time, or even by having a shot hit the net-cord and drop over, come off my racquet frame at an unlikely but advantageous angle, or bounce strangely for Roger.  But, the chance I'd win an entire game is maybe 0.1% (?), a set would be like winning lotto twice in a row, and a match - well, the universe might end first. (Sane caveats re Roger being mentally/physically fine etc..)</p>

<p>The more a game requires a great many moves to shape and turn the outcome, and the lower the chance for a fluke beyond either players' control, the more predictable the outcomes are, and the more the skill differential ensures the outcome, even if that skill is probabilistic and not deterministic.  Skill is a huge factor in chess, but skill is not a constant for a player - they may be more skillful at handling play from certain positions than others (perhaps they just read a book on a relevant tactic), and occasionally a player of lower average skill might prevail based on some particularly relevant but limited skill (and be deemed lucky that play led to a situation where they could apply it).  In close matches, and perhaps in beginner's matches where more of the movements are made arbitrarily without even a guiding strategy or heuristic used, luck starts to play a significant role.</p>

<p>I think it's interesting to compare this to baseball, I read a book about it years ago that explained how some Wall Street quant types crunched the maths and found that the worst team in the top league had something like half the chance of being the champions that the best team had... i.e. surprisingly little impact on odds came from achievable differences in skill (given the top team had vastly more budget to hire players considered "stars").  For example, while the percentage of swings that made contact varied with batter, the out/1st-base/2nd-base/3rd-base/home outcomes were in similar proportions: you might observe that it took skill to hit the ball more often, but doing so was so difficult and the angle of contact so uncontrollable that what happened when you did basically came down to luck.  Overall, luck could easily swing a game.</p>

<p>Separately, and this may be controversial and I'm not claiming it's true - just reasoning about the implications if it happens to be true:  I saw a study report that when chess grandmasters played good club players, starting at random board positions that would not occur during actual games: the grandmasters lost their main advantage as they didn't have a huge wealth of applicable reference games with which to compare; reduced to actual logical reasoning without any particular advantage - they only had a smidge more than 50/50 chance of a win.  Does that mean chess is less about skill than my above assertions imply?  Is a vast memory of games itself a skill?  I'd say so - it clearly allows you to "do well" in non-random games, and that's all the OED requires.  Further, consider say a language translator - we'd consider the size of their vocabulary to be an aspect of their skill level.</p>
 291: <p>By the commonly accepted definition of "game of skill", chess is 100% a game of skill. It has no random element at all and both players have full information about the game state at all times. Players do say things like "I was lucky that my opponent blundered", but that's not what is generally meant when people talk about "games of chance".</p>
 167: <p>If we remove the component of flawed, human players from the equation and consider just the game of chess itself as it is spelled out by the rules, then chess is purely a game of skill with no room for chance. That is, it is in principle possible for there to be a perfect chess player that plays optimally against every possible move sequence by an opponent, and that perfect player would never falter due to chance or luck. Such perfect players already exist at the level of chess positions with only a handful of pieces: <a href="http://en.wikipedia.org/wiki/Endgame_tablebase">endgame tablebases</a> consist of all the information necessary for perfect play in those positions, and if you play from such a position against an opponent with access to those tablebases, chance can play no role in stopping them from getting their deserved result.</p>

<p>However, the problem of computing a tablebase for the starting position of chess, with its 32 pieces, is far, far from tractable. So while optimal play does exist for all positions in chess, nobody knows for sure what optimal play is for the vast, vast majority of positions. Looked at in that light, when two humans (or even strong chess engines) play a game against one another, something that can reasonably be viewed as chance (for one side at least) can definitely play a role, but for what I have in mind at least, the root cause of any outcome is still skill (or its temporary absence).</p>

<p>Here's an example of what I mean. In the recent Zurich Chess Challenge, Nakamura was playing a fine <a href="http://www.chessgames.com/perl/chessgame?gid=1745310">game against Carlsen</a>, to the point where he had an overwhelming, winning advantage. At that point, it could safely be said that Carlsen "deserved" to lose.</p>

<pre><code>[fen "4r1k1/1p3pPp/6q1/2pPpNP1/p1n1P3/P6Q/7R/K7 w KQkq - 0 1"]
[White "Nakamura, Hikaru"]
[Black "Carlsen, Magnus"]
[Event "Zurich Chess Challenge"]
[Result "0-1"]

1.d6? (1.Qf1!)
</code></pre>

<p>But Nakamura made a crucial mistake that let Carlsen off the hook, later followed by further poor play that even allowed Carlsen to win. If someone were to say, "Carlsen was <em>lucky</em> to win that day," I'd say there's truth to that. (Carlsen certainly deserves credit for defending in such a way that Nakamura could still go wrong, but even so, he was fortunate that Nakamura erred as he did.) But the luck from Carlsen's side originated from nothing more than a momentary lack of skill on Nakamura's part. Finding the right move was entirely within Nakamura's power, but he wasn't quite skillful enough to find it in that moment.</p>

<p>As in most human endeavors, there is some element of chance in the competitive results of chess games. But that luck for one side generally comes in the form of what kind of lack of skill one's opponent shows (and when).</p>
