In music theory, a comma is a small or very small interval between two notes which, though it is almost not to be heard, is introduced by computing their frequencies.

There are many commas, notably :

• Pythagorean comma or ditonic comma (ratio between 7 justly tuned octaves and 12 justly tuned fifths. Its value is 3¹²:2¹⁹ or 531441:524288. The best approximative value in the form of (n+1)/n (n integer) is 74:73, which is sometimes used.
• syntonic comma
• schisma is the interval between Pythagorean comma and syntonic comma