The traditional measure of pitching performance is earned run average. It is calculated as earned runs allowed per 9 innings. Earned run average does not separate the ability of the pitcher from the abilities of the fielders that he plays with. Another classic measure for pitching is a pitcher's winning percentage. Winning percentage is calculated by dividing wins by the number of decisions (wins and losses). Winning percentage is also heavily dependent on the pitcher's team, particularly on the number of runs it scores.