About us

This is a free, independent site. It helps players, parents, coaches and scorekeepers work out ERA, WHIP, batting average, slugging, on base percentage and OPS. It is run by a small team of baseball fans and web developers.

How we check the math

Every formula comes from Rule 9.21 of the Official Baseball Rules, published by MLB. At bats follow Rule 9.02(a), and innings pitched follow Rule 9.02(c), which counts each out as one third of an inning. Our code runs a test suite before each release. It checks that 6.1 innings means 6 and 1/3, that 6.3 is rejected, and that the rule book example of 3 earned runs in 9 1/3 innings gives a 2.89 ERA.

League averages come from Baseball-Reference. Game lengths come from NFHS and Little League rules. We do not invent numbers, and every fact links to its source.

Independence

We are not linked to MLB, NFHS, the NCAA, Little League or any team or brand. Your league's scorer and rules always come first.

Updates

Last updated October 21, 2026. Found a mistake? Please tell us.

References

1. Official Baseball Rules 2025 (PDF), Rules 9.02, 9.21 and 9.22, Major League Baseball
2. Earned Run Average (ERA), MLB.com Glossary
3. Innings Pitched (IP), MLB.com Glossary
4. Major League Batting Year by Year Averages, Baseball-Reference
5. Major League Pitching Year by Year Averages, Baseball-Reference
6. Baseball Rules, Rule 4-2-2 Ending a Regulation Game, NFHS
7. Regulation VII: Making a Regular Season Schedule, Little League