Batting and pitching statistics
Baseball statistics explained: AVG, OBP, SLG, OPS, ERA and WHIP
A practical guide to common batting and pitching rate statistics, how their formulas differ, and what the numbers do and do not tell you.
AVG, at-bats and plate appearances
Batting average (AVG) is hits divided by at-bats: AVG = H / AB. An at-bat is not the same as a plate appearance (PA). Walks, hit-by-pitches and some sacrifices can produce a plate appearance without adding an at-bat, so PA is usually larger than AB.
OBP, SLG and OPS
On-base percentage (OBP) measures how often a batter reaches base through results counted by the formula, including hits, walks and hit-by-pitches. Slugging percentage (SLG) is total bases divided by at-bats, giving more weight to extra-base hits. OPS is simply OBP + SLG.
ERA and innings pitched
Earned run average (ERA) expresses earned runs allowed per nine innings: ERA = 9 × ER / IP. Innings pitched are built from outs: each out is one-third of an inning. In common baseball notation, 5.1 IP means five and one-third innings and 5.2 means five and two-thirds, not decimal tenths.
WHIP and statistical context
WHIP = (BB + H) / IP: walks plus hits allowed divided by innings pitched. Lower WHIP generally means the pitcher allowed fewer baserunners by those two routes. Hit batters, errors and fielder’s choices are not included in WHIP, and no single statistic completely describes a hitter or pitcher.