What is Isolated Power (ISO) in baseball?

Asher Hyre Updated: Sep 16 2025 22:07

The MLB playoffs are right around the corner and stats will be discussed to divvy up awards, making this an ideal time to talk about this advanced statistic.

Isolated power (ISO) is a lesser-used stat than the more encompassing AVG, OPS, or SLG stats.

ISO uses extra-base hits to tell us just how much raw power a player has.

This article will explain how ISO is calculated, explain the origins of ISO, and give you the career and single season leaders for ISO.

How is Isolated Power (ISO) calculated?

As stated before, ISO only takes into account extra base hits and what type of extra base hit it is.

ISO is a simple statistic and can be calculated in two different ways. The first way is the formula:

Formula: (1x2B + 2x 3B + 3xHR) / At-bats = ISO

In a scenario where a player is 2-for-5 with two singles, his ISO would be .000.

In a scenario where a player is 2-for-5 with a double and a single, his ISO would be .200.

The second method of calculating ISO is very simple:

Formula: SLG - AVG = ISO

Simply subtract a player's slugging number by their average number and you have ISO.

Origins of Isolated Power (ISO) in baseball

Branch Rickey broke the color barrier by making Jackie Robinson the first black player to play in MLB. His statistician at the time, Allan Roth, sought to measure a player's raw power beyond the traditional statistics of AVG and SLG and developed the underlying concepts for ISO.

Baseball journalist Bill James officially coined the term "isolated power."

MLB Career Isolated Power (ISO) Leaders

Player	ISO
Babe Ruth	.348 (1914-1935)
Mark McGwire	.325 (1986-2001)
Aaron Judge	.321 (2016-present)
Barry Bonds	.309 (1986-2007)
Shohei Ohtani	.298 (2018-present)

MLB Single-Season Isolated Power (ISO) Leaders

Player	ISO
Barry Bonds	.536 (2001)
Babe Ruth	.472 (1920)
Babe Ruth	.469 (1921)
Mark McGwire	.454 (1998)
Barry Bonds	.450 (2004)