How ERA works
Earned run average measures how many earned runs a pitcher allows per nine innings. The formula is
simply ERA = (ER / IP) × 9. The multiply-by-nine step is what converts a raw rate into
the familiar per-nine-innings figure, because a standard game is nine innings long. As a guide,
an ERA under 3.00 is excellent, around 4.00 is roughly average,
and above 5.00 is a struggling line.
The .1 / .2 innings convention
Innings pitched are tracked in thirds, one for each out, so the decimal part of an IP figure is
not a normal fraction. A trailing .1 means one out (⅓ of an inning) and
.2 means two outs (⅔ of an inning). That is why 6.2 IP is really
6 and two-thirds innings, or 6.667 for the arithmetic — not 6.2. This calculator converts those
endings automatically before dividing, and you can also type a plain decimal such as 6.667 if you
already have it.
How to read the result
ERA only counts earned runs — runs that score because of an error or passed ball are unearned and excluded — so it isolates run prevention the pitcher is responsible for. It still carries some defense, ballpark and sequencing noise, which is why analysts pair it with fielding independent pitching. Read the full breakdown of ERA in baseball, and see what FIP is for the defense-independent companion metric.
Frequently asked questions
How is ERA calculated?
Earned run average is earned runs divided by innings pitched, multiplied by nine: ERA = (ER / IP) × 9. The × 9 puts the figure on a standard nine-inning basis, so ERA reads as 'earned runs allowed per nine innings.' A pitcher who gives up 3 earned runs in 9 innings has a 3.00 ERA; the same 3 earned runs in 6 innings is a 4.50 ERA. Only earned runs count — runs that score because of an error or passed ball are unearned and excluded.
How do you enter innings pitched with the .1 and .2 endings?
In baseball, innings pitched are recorded in thirds because each out is one-third of an inning. A trailing .1 means one out (⅓ of an inning) and .2 means two outs (⅔ of an inning) — they are not tenths. So 6.2 IP means 6 and two-thirds innings, which equals 6.667 for the math. This calculator converts a .1 ending to +⅓ and a .2 ending to +⅔ automatically before dividing. If you already have the decimal value (for example 6.667), you can type that in directly.
What is a good ERA?
As a rule of thumb, an ERA under 3.00 is excellent, around 4.00 is roughly league average in the modern game, and above 5.00 is poor. Sub-2.00 over a full season is ace, award-contending territory. The benchmarks drift with the run environment — ERAs across the league rise in high-offense eras and fall in pitching-friendly ones — so ERA is best read against the league average of its own season rather than as a fixed number.
What counts as an earned run?
An earned run is a run that scores without the help of a fielding error or a passed ball — in other words, a run the pitcher is held responsible for. If a batter reaches on an error and later scores, or a run scores only because of a misplay that should have ended the inning, that run is 'unearned' and does not count toward ERA. Because ERA excludes unearned runs, it isolates run prevention that is more attributable to the pitcher than to the defense behind them.
What are the limits of ERA, and what is FIP?
ERA still blends in things a pitcher does not fully control — the defense's range, ballpark, and sequencing luck with runners on base. FIP (Fielding Independent Pitching) was built to strip those out: it uses only strikeouts, walks, hit-by-pitches and home runs — the outcomes a pitcher most directly controls — and scales the result to look like an ERA. When a pitcher's ERA and FIP diverge sharply, FIP is often the better guide to how they will pitch going forward. See the FIP explainer linked below for the formula.