OPS rescaled against the league average for the same season, so 100 is exactly league average and 150 means 50% better than average. Because each season is measured against its own league, OPS+ compares hitters across eras. As published by Baseball-Reference it is also adjusted for the player's home ballparks.
Adjusted OPS (OPS+)
Also written: OPS+
Standard statistic · MLB
Formula
OPS+ = 100 × (OBP ÷ lgOBP + SLG ÷ lgSLG − 1) (Baseball-Reference additionally divides by a park factor.)
On StatVault
Computed in-house per season and per league — AL, NL and each historical and Negro league measured separately — from the season lines in the corpus. It is park-unadjusted (the corpus carries no park factors), and the on-base term uses (H + BB) ÷ (AB + BB) for both player and league because the source feed has no HBP or SF. Shown on MLB profiles' advanced table and ranked on the MLB Advanced boards.
Shown on: MLB player profiles — advanced table