Isolated Power (ISO)
Also known as: ISO, isolated slugging, raw power stat
Isolated power (ISO) measures a hitter's extra-base power: slugging percentage minus batting average. You can also figure it as doubles plus twice the triples plus three times the home runs, divided by at-bats. In MLB, about .140 is league average, .200 is great and .250 is excellent.
Batting average counts every hit the same. Slugging percentage gives more credit for extra bases. ISO subtracts one from the other, so singles drop out and only doubles, triples and home runs count. A hitter with 100 at-bats, 6 doubles, 1 triple and 4 home runs has an ISO of (6 + 2 + 12) ÷ 100, or .200.
FanGraphs' rule-of-thumb scale for MLB runs from about .080 (awful) through .140 (average) to .250 (excellent), and the league average shifts from year to year. Youth and high school numbers sit on different scales because of field size, bats and pitching. As a result, compare a player with others in his own league.
ISO also needs a big sample. FanGraphs says it takes about 550 plate appearances, roughly a full MLB season, before ISO starts to predict future ISO.
Tips by skill level
Work out your ISO at the end of the season by subtracting your batting average from your slugging percentage. Then set a goal to raise it by driving more balls into the gaps.
Pair ISO with exit velocity and launch angle. A low ISO with strong exit velocity usually means too many ground balls. At the same time, a low ISO with weak exit velocity points to a strength or bat-speed gap.
Example
Two high school hitters both bat .300. One has an ISO of .060 because almost every hit is a single. The other has an ISO of .220 from doubles and home runs. The coach bats the second hitter third and asks the first to work on driving the ball into the gaps.
Why it matters
ISO separates contact from power. Two hitters with the same average can bring very different value, and ISO shows which one drives the ball for extra bases.
Common mistakes
- Comparing a youth player's ISO with MLB benchmarks
- Judging ISO after a few weeks, when it needs hundreds of plate appearances
- Dividing by plate appearances instead of at-bats in the formula
Frequently asked questions
What is a good ISO in baseball?
On FanGraphs' MLB scale, about .140 is average, .200 is great and .250 is excellent. Youth and high school numbers vary by league, so compare within the same level.
How do you calculate isolated power?
Subtract batting average from slugging percentage. Or add doubles, two times triples and three times home runs, then divide by at-bats.
What is the difference between ISO and slugging percentage?
Slugging counts singles as well as extra-base hits. ISO removes the singles, so it measures only extra-base power.
Sources
Related terms
- On-Base Plus Slugging (OPS)OPS is a hitting stat that adds on-base percentage and slugging percentage. It combines reaching base and hitting for power in one number.
- Weighted On-Base Average (wOBA)Weighted On-Base Average (wOBA) gives each hitting outcome a run value. It combines walks and hits into one rate that is scaled like on-base percentage.
- BABIP (Batting Average on Balls in Play)BABIP is batting average on balls in play: hits that are not home runs, divided by the balls a hitter puts in play. The formula is (H − HR) ÷ (AB − K − HR + SF). League average is almost always around .300. Line drives fall for hits more often than ground balls, and ground balls more often than fly balls. As a result, hard line-drive contact helps. But short streaks are mostly luck.
- Exit Velocity (EV)Exit velocity is how fast the ball comes off the bat, in mph. It is a ceiling metric — the harder you hit it, the farther it can go.
- BarrelA barrel is a batted ball with both high exit velocity and an optimal launch angle. That combination is the one most likely to produce extra-base hits.
Related guides & benchmarks
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