OPS+ and ERA+: the 100 scale
One number, any era, any park: 120 means 20% better than the league. Ready?
'Plus' stats take a familiar stat, adjust for park and league scoring, and rescale so 100 = exactly average. OPS+ 130 → 30% better than the league's OPS environment. ERA+ flips direction so higher is always better: ERA+ 150 is ace territory.
Why the scale is addictive
It makes eras comparable: a .900 OPS in 2000's launching-pad environment and one in a dead-ball year mean totally different things, but OPS+ puts both on the same ruler. It also makes conversation instant — 'he's a 140 hitter' needs no context.
These are Baseball-Reference's flavors, built on OPS's crooked weights — so OPS+ inherits the undervalued-OBP flaw. Level 3's wRC+ does the same job with correct weights; when the two disagree slightly, wRC+ is righter. The 100-scale idea, though, is the keeper: you'll see it everywhere from here on.
The formula (optional — skippable)
OPS+ ≈ 100 × (OBP/lgOBP + SLG/lgSLG − 1), park-adjusted
lg = league average that season. The real formula has more plumbing; the idea is 'you vs your environment'.
How this stat lies to you
- Inherits OPS's flaw (OBP undervalued) — wRC+ fixes this at Level 3.
- League-average baseline includes pitchers batting in old eras — cross-era comparisons have asterisks.
- 100 = average for the LEAGUE, not for a position — a 100 OPS+ catcher is valuable, a 100 first baseman less so (Level 5).
Check yourself
1. ERA+ of 125 means…
2. Why can you compare OPS+ across decades but not raw OPS?