Hong Life CalculatorsUnderstanding the wOBA calculator — concept and principle
Weighted on-base average (wOBA) measures a hitter's total offensive value per plate appearance, giving each way of reaching base a weight equal to its average run value. It was introduced by Tom Tango and colleagues in The Book and is published by FanGraphs; analysts prefer it to OPS when they want one number that reflects how hitting events actually create runs.
How it is calculated
wOBA = (0.691 uBB + 0.722 HBP + 0.882 1B + 1.252 2B + 1.584 3B + 2.037 HR) / (AB + uBB + SF + HBP)
- uBB is unintentional walks, the total walks minus intentional walks (IBB).
- The denominator equals AB + BB − IBB + SF + HBP, the standard FanGraphs form; intentional walks are left out of both parts, so there is no IBB field.
- The weights are the FanGraphs Guts values for the 2025 season: linear-weight run values rescaled so that league wOBA is on the same scale as league OBP. They change a little every season.
The principle
Linear weights come from run-expectancy tables: for every base-out situation, analysts know how many runs a team scores on average from that point to the end of the inning. The average change in run expectancy caused by a single, double, walk and so on is that event's run value. wOBA adds an out's cost back so the values are relative to an out, then scales them up so the final number looks like OBP. A home run is therefore worth roughly 2.3 singles in wOBA, not 4 as in slugging, and a walk is worth most of a single, which OPS undervalues.
Worked example
- Inputs: 60 uBB, 5 HBP, 100 1B, 30 2B, 3 3B, 25 HR, 500 AB, 5 SF.
- Numerator: 0.691×60 + 0.722×5 + 0.882×100 + 1.252×30 + 1.584×3 + 2.037×25 = 41.46 + 3.61 + 88.2 + 37.56 + 4.752 + 50.925 = 226.507.
- Denominator: 500 + 60 + 5 + 5 = 570.
- wOBA = 226.507 / 570 = .3974.
| AB | wOBA |
|---|---|
| 125 | 1.161574359 |
| 250 | 0.707834375 |
| 375 | 0.5090044944 |
| 500 | 0.3973807018 |
| 625 | 0.3259093525 |
| 750 | 0.2762280488 |
| 1,000 | 0.211688785 |
How to read the result
League-average wOBA sits close to league-average OBP, usually around .310–.320. FanGraphs' rule-of-thumb scale treats about .320 as average, .340 above average, .370 great and .400 excellent, so .397 is a great season, just short of excellent. To turn wOBA into runs, analysts compute wRAA = (wOBA − league wOBA) / wOBA scale × PA, using the season's scale factor.
Common mistakes
- Including intentional walks in uBB.
- Using weights from a very different season or league (for example a minor league or the KBO) without adjusting.
- Comparing wOBA across parks; wRC+ adjusts for park and league.
Frequently asked questions
Why are intentional walks excluded?
They reflect the defence's choice more than the hitter's skill, so wOBA leaves them out of both parts of the formula.
Is wOBA better than OPS?
It weights events by their real run value and uses a single denominator, so it tracks run scoring a little better and is easier to interpret.
Why does a single count 0.882, not 1?
The weights are run values scaled to look like OBP, not base counts.
Sources: Tom Tango, Mitchel Lichtman and Andrew Dolphin, The Book: Playing the Percentages in Baseball (2007) · FanGraphs Library, wOBA; FanGraphs Guts! (season constants)