ERA Calculations for Varying Innings per Game

Submitted by Frank on 04/05/2009

When it comes to Baseball ERAs there seems to be a lot of confusion around how to calculate the statistic if your league does not use 9 inning games. The ERA statistic is defined as follows:

ERA = 9 x (Earned Runs Allowed/Innings Pitched)

Many people believe that the 9 is actually the number of innings per game. MLB uses 9 innings, therefore the statistic shows you how many earned runs a pitcher would give up on average if they pitched a full game. This does not hold true for leagues that use 6 or 7 innings per game.

An ERA for Little League should be comparable to an ERA for Major League Baseball. Let's look at an example...

A pitcher pitches 9 full 6 inning games (54 Innings) and lets say this pitcher lets up 9 earned runs across those 9 games. If we use a 9 in the ERA equation, the pitcher's ERA is 1.50. If we use 6 in the ERA equation, the pitcher's ERA is 1.00.

When you look at the example above it shows that this statistic would return different values if you allowed people to enter in different inning's per game. The ERA statistic is defined with a 9 so that any ERA can be compared directly against another without wondering what "inning's per game" they used to compute it.

Softball is a different story because the highest softball league in the United States uses a 7 instead of a 9. Since most softball leagues use 7 innings, TomorrowsPro has followed the trend for this sport and our softball ERA is defined as follows:

ERA (Softball) = 7 x (Earned Runs Allowed/Innings Pitched)

With all this being said we are looking into adding ERA6 and ERA7 categories in the future.