What is ERA?
Earned Run Average (ERA) is the classic measure of a pitcher's effectiveness in baseball and softball. It expresses the average number of earned runs a pitcher would give up over a full game's worth of innings. A lower ERA means a more effective pitcher. Only earned runs count — runs that score because of fielding errors or passed balls are excluded.
How to use this calculator
Enter the number of earned runs (ER) the pitcher allowed, the number of full innings pitched, and pick how many outs were recorded in any incomplete final inning (0, 1 or 2). Then choose the game length: 9 innings for standard baseball, 7 for softball, or 6 for Little League. The calculator returns the ERA rounded to two decimal places.
The formula explained
ERA is computed as:
$$\text{ERA} = \dfrac{\text{ER} \times \text{Innings per Game}}{\text{IP}}$$
where innings pitched (IP) = full innings + outs/3. Because each out equals one-third of an inning, this calculator asks for the raw number of outs to avoid the confusing "6.1 = 6â…“" decimal notation used on scoreboards.
Worked example
A baseball pitcher allows 3 earned runs over 6 full innings plus 2 outs (6â…” innings). \(\text{IP} = 6 + 2/3 = 6.6667\). $$\text{ERA} = \dfrac{3 \times 9}{6.6667} = \dfrac{27}{6.6667} = 4.05$$
FAQ
What counts as an earned run? A run the pitcher is responsible for without help from defensive errors or passed balls. Unearned runs are not included in ERA.
What if 0 innings were pitched? If a pitcher records no outs but allows earned runs, ERA is mathematically undefined (often shown as "INF"). This calculator displays an undefined message instead of dividing by zero.
Why choose innings per game? The multiplier scales the rate to a full game. Baseball uses 9, softball 7, and Little League 6, so selecting the right league gives an accurate, comparable ERA.
