Isolated Power

In baseball, Isolated Power or ISO is a sabermetric computation used to measure a batter's raw power. One formula is slugging percentage minus batting average.

I S O = S L G − A V G

= ( 1 B ) + ( 2 × 2 B ) + ( 3 × 3 B ) + ( 4 × H R ) A B − H A B

= ( 1 B ) + ( 2 × 2 B ) + ( 3 × 3 B ) + ( 4 × H R ) − ( 1 B + 2 B + 3 B + H R ) A B

= ( 2 B ) + ( 2 × 3 B ) + ( 3 × H R ) A B

The final result measures how many extra bases a player averages per at bat. A player who hits only singles would thus have an ISO of 0. The maximum ISO is 3.000, and can only be attained by hitting a home run in every at-bat.

The term "Isolated Power" was coined by Bill James, but the concept dates back to Branch Rickey and his statistician Allan Roth.