[Justin M]

Thanks kh99!

per predictem

Add up a pitchers innings. An inning is three outs. If you see 6.1 or 6.2 that means 6.33 or 6.67 innings. Unlike some other baseball stats, we don't round up when we're talking about ERA.

Now add up all the earned runs the pitcher gave up during the innings he's pitched. For arguments sake, lets say he gave up 3 earned runs.

Now multiply the earned runs by 9.

Now divide by the total innings pitched.

Example: A pitcher goes 5 innings and gives up 3 earned runs. We take the earned runs x 9 which gives us 27. We then divide this by the innings pitched 27 divided by 5 = 5.40.
In case you're wondering what the good, bad and the ugly are ERA-wise in the big leagues it could be said that:

An earned run average of 2.00 or lower is an ace and a very sharp pitcher. Anything 3.00 or under is ROCK solid. An ERA of 3.00 to 3.50 is GOOD. Conversely, 4.00 to 5.00 is average and anything above 5.00 a guy is probably struggling to stay in the bigs and is getting hit pretty hard.

If you can figure out how to make the users posts go along with the time registered to show the ERA (I think I'm on the right path), that is pure genius. I'm not that good with equations.

mokujin, ERA or earned run average, is another way of saying "what a pitcher gives up per nine innings that he pitches."