Kurtosis is based on the size of a distribution's tails. Distributions with relatively large tails are called "leptokurtic"; those with small tails are called "platykurtic." A distribution with the same kurtosis as the normal distribution is called "mesokurtic."

The following formula can be used to calculate kurtosis:

kurtosis formula

where σ is the standard deviation. The kurtosis of a normal distribution is 0.

The following two distributions have the same variance, approximately the same skew, but differ markedly in kurtosis.