text: user4983: In bioinformatics, a sequence logo is a graphical representation of the sequence conservation of nucleotides (in a strand of DNA/RNA) or amino acids (in protein sequences).
  wiki says
  
  The total height of the letters depicts the information content of the
    position, in bits.
  
  and then gives this example
  
  A sequence logo showing the most conserved bases around the initiation
    codon from all human mRNAs (Kozak consensus sequence). Note that the
    initiation codon is not drawn to scale, otherwise the letters AUG
    would each have a height of 2 bits.
  
  
  it seems that there is a 0.1 bit letter.
  is this in the context of 2bits? is 2bits the highest bits in this sequence logo? Is there a convention or standard of the highest bits in a sequence logo?
  
  user298: This is explained in the original paper [1] describing the logos (emphasis mine):
  
  The importance of a particular position in a binding site is more clearly
    and consistently given by the information required to describe the pattern
    there [7, 8]. To choose one symbol or state from two equally likely possibilities
    requires one "bit" of information. For example, to communicate the result of
    a coin-ip to someone requires 1 bit of information because only one yes-no
    question needs to be answered: "Is it heads?". If a position in a binding
    site always contains one base (e.g. G), then we need exactly two bits of
    information since two yes-no questions need to be answered: "Is it A or G?"
    (i.e. is it a purine?) and "Is it A or C?". (If the answers to both questions
    are "no", it must be a T.) Furthermore, if a position contains two bases (e.g.
    sometimes A and sometimes G), only one question suffices since a two out of
    four choice is equivalent to a one out of two choice. Therefore, only one bit
    is needed to describe a position in a binding site that contains only purines,
    but two bits are needed to describe a position that always contains adenine.
  
  So yes, 2bits is the highest value you will see on the y-axis of a DNA sequence logo (proteins are a different story since there are more possibilities). In the one you show, the scale is from 0 to 0.2, but it's the same principle. 
  However, you should think of logos as a useful visual aid, and not a way of getting rigorous mathematical information about a sequence. So don't put too much weight on the bit values. If you need that sort of data, calculate it from the alignment directly. 
  
  [1] Schneider TD, Stephens RM., Sequence logos: a new way to display consensus sequences., Nucleic Acids Res. 1990 Oct 25;18(20):6097-100.
  
original_text: 4983: <p>In bioinformatics, a <a href="https://en.wikipedia.org/wiki/Sequence_logo" rel="nofollow noreferrer">sequence logo</a> is a graphical representation of the sequence conservation of nucleotides (in a strand of DNA/RNA) or amino acids (in protein sequences).</p>
  
  <p>wiki says</p>
  
  <blockquote>
    <p>The total height of the letters depicts the information content of the
    position, in bits.</p>
  </blockquote>
  
  <p>and then gives this example</p>
  
  <blockquote>
    <p>A sequence logo showing the most conserved bases around the initiation
    codon from all human mRNAs (Kozak consensus sequence). Note that the
    initiation codon is not drawn to scale, otherwise the letters AUG
    would each have a height of 2 bits.</p>
  </blockquote>
  
  <p><a href="https://i.stack.imgur.com/eA1L0.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/eA1L0.png" alt="e"></a></p>
  
  <p>it seems that there is a 0.1 bit letter.</p>
  
  <p>is this in the context of 2bits? is 2bits the highest bits in this sequence logo? Is there a convention or standard of the highest bits in a sequence logo?</p>
   298: <p>This is explained in <a href="https://www.ncbi.nlm.nih.gov/pubmed/2172928" rel="nofollow noreferrer">the original paper</a> [1] describing the logos (emphasis mine):</p>
  
  <blockquote>
    <p>The importance of a particular position in a binding site is more clearly
    and consistently given by the information required to describe the pattern
    there [7, 8]. To choose one symbol or state from two equally likely possibilities
    requires one "bit" of information. For example, to communicate the result of
    a coin-ip to someone requires 1 bit of information because only one yes-no
    question needs to be answered: "Is it heads?". <strong>If a position in a binding
    site always contains one base (e.g. G), then we need exactly two bits of
    information since two yes-no questions need to be answered: "Is it A or G?"
    (i.e. is it a purine?) and "Is it A or C?". (If the answers to both questions
    are "no", it must be a T.)</strong> Furthermore, if a position contains two bases (e.g.
    sometimes A and sometimes G), only one question suffices since a two out of
    four choice is equivalent to a one out of two choice. Therefore, only one bit
    is needed to describe a position in a binding site that contains only purines,
    but two bits are needed to describe a position that always contains adenine.</p>
  </blockquote>
  
  <p>So yes, 2bits is the highest value you will see on the y-axis of a <strong><em>DNA</em></strong> sequence logo (proteins are a different story since there are more possibilities). In the one you show, the scale is from 0 to 0.2, but it's the same principle. </p>
  
  <p>However, you should think of logos as a useful visual aid, and not a way of getting rigorous mathematical information about a sequence. So don't put too much weight on the bit values. If you need that sort of data, calculate it from the alignment directly. </p>
  
  <hr>
  
  <p>[1] Schneider TD, Stephens RM., Sequence logos: a new way to display consensus sequences., <em>Nucleic Acids Res.</em> 1990 Oct 25;18(<strong>20</strong>):6097-100.</p>
  