Isolated Power (ISO) Calculator
Calculate a hitter’s isolated power (ISO = SLG − AVG) from at-bats, hits, doubles, triples and home runs, with batting average, slugging and the FanGraphs ISO rating scale.
How it works
ISO = SLG − AVG = (2B + 2 × 3B + 3 × HR) ÷ AB · AVG = H ÷ AB · SLG = (H + 2B + 2 × 3B + 3 × HR) ÷ AB.
Isolated power measures raw extra-base power: the extra bases a hitter collects beyond first base on each hit, per at-bat. Subtracting batting average from slugging removes singles, so a slap hitter with a high average no longer looks like a power bat. FanGraphs’ rule of thumb rates .250 excellent, .200 great, .140 average and .080 awful.
Worked example
A hitter with 550 at-bats, 160 hits, 32 doubles, 3 triples and 25 home runs has 32 + 2 × 3 + 3 × 25 = 113 extra bases. ISO = 113 ÷ 550 = .205 (Great). His AVG is .291 and SLG .496, and .496 − .291 = .205 confirms it.
Sources: FanGraphs Sabermetrics Library — ISO · MLB.com Glossary — Isolated Power (ISO)
Frequently asked questions
What is a good ISO in baseball?
FanGraphs’ scale: .250+ excellent, .200 great, .170 above average, .140 average, .120 below average, .100 poor and .080 or lower awful. Elite sluggers post .300+.
Why subtract batting average from slugging?
Slugging counts a single as one base, so it rewards contact hitters as well as power. Taking away AVG leaves only the extra bases from doubles, triples and home runs.
Can ISO be higher than batting average?
Yes. A low-average slugger who hits .230 with lots of home runs can have an ISO of .260, which is higher than his average.
Is ISO the same as XBH%?
No. Extra-base-hit percentage counts how many hits went for extra bases; ISO also weights them, so a home run counts three times as much as a double.
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This calculator is for educational purposes. Double-check important results before acting on them.