Weighted On-Base Average (wOBA) is one of the most important and popular catch-all offensive statistics. It was created by Tom Tango (and notably used in “The Book”) to measure a hitter’s overall offensive value, based on the relative values of each distinct offensive event.
wOBA is based on a simple concept: Not all hits are created equal. Batting average assumes that they are. On-base percentage does too, but does one better by including other ways of reaching base. Slugging percentage weights hits, but not accurately (Is a double worth twice as much as a single? In short, no). On-base plus slugging (OPS) does attempt to combine the different aspects of hitting into one metric, but it assumes that one percentage point of SLG is the same as that of OBP. In reality, a handy estimate is that OBP is around twice as valuable than SLG (the exact ratio is x1.8).
Weighted On-Base Average combines all the different aspects of hitting into one metric, weighting each of them in proportion to their actual run value. While batting average, on-base percentage, and slugging percentage fall short in accuracy and scope, wOBA measures and captures offensive value more accurately and comprehensively.
The wOBA formula for the 2012 season was:
wOBA = (0.691×uBB + 0.722×HBP + 0.884×1B + 1.257×2B + 1.593×3B +
2.058×HR) / (AB + BB – IBB + SF + HBP)
These weights change on a yearly basis, so you can find the specific wOBA weights for every year from 1871 to 2010 here.
Please note that the following chart is meant as an estimate, and that league-average wOBA varies on a year-by-year basis. It is set to the same scale as OBP, so league-average wOBA in a given year should be very close to the league-average OBP. To see the league-average wOBA for every year from 1901 to the present, check the FanGraphs leaderboards.
Rules of Thumb
● This stat accounts for the following aspects of hitting: unintentional walks, hit-by-pitches, singles, doubles, triples, home runs. Stolen-bases and caught stealing numbers used to be included as well on FanGraphs, but they are now instead accounted for with the stats UBR and wSB. This way, wOBA accounts for just a player’s production at the plate.
● Exactly how much to weigh each of the components of wOBA was determined using linear weights.
● wOBA can be converted into offensive runs above average easily. These are called Weighted Runs Above Average (wRAA). The formula to convert wOBA into wRAA is listed below:
● This stat is context-neutral, meaning it does not take into account if there were runners on base for a player’s hit or if it was a close game at the time.
● wOBA on FanGraphs is not adjusted for park effects, meaning that batters that play in hitter-friendly parks will have slightly inflated wOBAs.