Earned run average calculator.

Multiply earned runs by nine, then divide by innings pitched. The nine scales everything to a full game, which is why ERA reads as "runs allowed per nine innings".

Baseball writes thirds as .1 and .2 — enter 180.2 for 180⅔ innings. The calculator converts to outs under the hood, so the fraction is exact, not a rounding.

The modern league average floats around 4.00. Under 3.00 is a solid front-line starter, under 2.00 is historic — Bob Gibson’s 1.12 in 1968 literally forced baseball to lower the mound.

Runs that score because of errors or passed balls are unearned and excluded. That is the point of the stat: it tries to isolate what the pitcher gave up on his own.

By raw ERA no — 1.74 against 1.12. Against their leagues, yes: Pedro’s 1.74 came in a season when the average team scored over five runs a game, the largest gap between a pitcher and his era on record.

ERA adjusted for the league and the ballpark, scaled so 100 is average and higher is better. It is the reason a 1.12 from a low-scoring year and a 1.74 from a high-scoring one can be argued about at all.

One inning per team game — 162 in a full season. A reliever can post the lowest ERA in baseball and never appear on the leaderboard, because the qualifying line is built for starters.

Walks and hits per inning pitched. It counts traffic rather than damage, so a pitcher who strands runners can carry a fine ERA on an ugly WHIP — and that gap is usually the first sign the ERA will not last.

They throw an inning at maximum effort against a fraction of the lineup, and they rarely face a hitter twice in a night. Judge a closer’s 2.10 against other relievers, never against a rotation.

Ed Walsh at 1.82, compiled entirely inside the deadball era when the whole league scored under four runs a game. Every name near the top of that list pitched before 1920, which is the clearest possible argument for reading ERA against its own time.

The trap is innings pitched. Baseball writes two-thirds of an inning as .2, but a spreadsheet reads that as two-tenths, so a plain =ER*9/IP is wrong on any partial inning. Convert first: =ER*9/(INT(IP)+(IP-INT(IP))*10/3) reads 180.2 as 180⅔ and returns the correct figure. For a seven-inning game — most high-school baseball and softball — replace the 9 with a 7.

Run environments moved so far that a 3.00 season has been anything from ordinary to league-leading depending on the decade. The archive from 1871 is the only honest comparison set.

Earned run average hides the defence behind the pitcher and the park around them both. Awards voted at the end of a season had all of that in view, which is why a pitcher fourth in ERA has sometimes collected more recognition than the man who led it.

Multiply by the length of a regulation game rather than always by nine. Softball and most high-school baseball run seven innings, so earned runs over innings pitched times seven is the correct figure there — using nine inflates it by about a third.