What Is ERA in Baseball? Formula & Innings Notation

The ERA formula

Earned Run Average estimates how many earned runs a pitcher allows per nine innings:

ERA = 9 × earned runs ÷ innings pitched
Example: 12 earned runs in 35.0 innings gives 12 × 9 ÷ 35 = 3.09.

Innings notation counts outs

Baseball does not use ordinary decimal tenths for partial innings. The suffix .1 means one out and .2 means two outs. Five innings and one out is therefore 5.1, or 16 outs. The third out completes the next whole inning, so 5.3 is invalid and should be 6.0.

Earned runs require official scoring

ERA uses earned runs, not every run that scores. Official scoring determines whether a run is earned and can charge a pitcher for a responsible baserunner who scores after that pitcher leaves.

There is no universal performance band

Lower ERA means fewer earned runs per nine innings, but league scoring, ballpark, defence, era, role and sample size affect interpretation. A fixed “good” or “bad” cutoff is not reliable across all contexts.

Use supporting statistics

ERA does not isolate pitching from every fielding or sequencing effect. WHIP, strikeout and walk rates, ERA+ and other measures can add context.

Frequently Asked Questions

What is the ERA formula?

ERA equals earned runs multiplied by nine, divided by innings pitched.

How do I enter one-third of an inning?

Use .1 for one out and .2 for two outs. These suffixes are baseball out notation, not decimal tenths.

Why is 6.3 innings invalid?

The third out completes the inning, so 6.3 must be recorded as 7.0.

Do unearned runs count in ERA?

No. ERA uses earned runs as determined by the official scorer.

What Is ERA in Baseball and How Is It Calculated?