How to Read Pitcher Stats: ERA, WHIP, K/9, BB/9 and K%

A pitcher's stat line packs a lot into a few columns. This guide walks through the ones you see on every box score and player page, with the official definition, the formula, one worked example and what counts as good. Definitions follow the MLB.com glossary and the FanGraphs Library.

First, how innings are written

Innings pitched (IP) count outs, three to an inning. The digit after the dot is outs, not tenths: 6.1 IP means 6⅓ innings and 6.2 means 6⅔. Convert before you divide, or every rate stat below comes out wrong. 180.2 IP is 180.667 innings.

ERA: earned runs per nine innings

MLB defines earned run average as the earned runs a pitcher allows per nine innings, where an earned run is one that scored without the aid of an error or a passed ball. Formula: ERA = 9 × earned runs ÷ innings pitched.

ERA is the result that matters to the scoreboard, but it mixes the pitcher with his defense, his ballpark and sequencing luck (whether the hits came together or spread out). That is why analysts pair it with the component stats below.

WHIP: base runners per inning

WHIP stands for walks plus hits per inning pitched. Formula: WHIP = (walks + hits) ÷ innings pitched (MLB glossary, FanGraphs). Lower is better. Hit batters and errors do not count, so WHIP slightly understates traffic for a pitcher who plunks a lot of hitters.

FanGraphs' rule-of-thumb scale: about 1.00 excellent, 1.10 great, 1.20 above average, 1.30 average, 1.40 below average, 1.50 poor and 1.60 awful. League average moves from year to year, so compare a pitcher with his own season.

Strikeout and walk rates: K/9, BB/9, K% and BB%

Worked example: one season line

Take a made-up starter: 180 IP, 740 batters faced, 150 hits, 60 earned runs, 45 walks, 5 hit batters, 190 strikeouts and 20 home runs.

That profile (a WHIP near 1.10, a strikeout rate in the mid-20s and a walk rate near 6%) is a good starter by FanGraphs' benchmarks, and the ERA agrees. When ERA and the component stats disagree, the components usually tell you more about the next month. Our explainer on FIP, xFIP and xERA shows how to turn them into an ERA-scale estimate.

Stats to read with caution

BullpenEdge's pitcher pages show these rates for every probable starter, and our projection model leans on strikeout and walk rates because they hold up better from start to start than ERA.