ERA
Earned run average — earned runs allowed per 9 innings.
What ERA means
The traditional pitching number. Heavily influenced by defense and luck (sequencing, BABIP) so FIP/xFIP/SIERA are usually preferred for true talent.
How ERA is calculated
ERA = (Earned Runs × 9) / IP
What counts as a good ERA
Lower is better — roughly 4.5 is poor, 4 average, 3.5 good, and 3 or better elite.
Also written
era_value · earned_run_avg