MLB ballpark data
The Coors Field humidor and altitude effect, measured
By OverUnderWeather Research Desk
How the humidor works, and what 471 Rockies home games from 2021 to 2026 show about scoring, home runs and the betting total compared with 13,628 games at every other park.
Quick answer
Extra runs per game
+2.43
11.25 vs 8.82 · d = 0.52
Extra home runs
+0.25
2.55 vs 2.3 · d = 0.15
Over rate vs closing total
48.8%
226 overs, 237 unders
Coors Field is still by far the highest-scoring park in baseball, but the humidor has largely done its job on home runs. The extra scoring now comes mostly from balls in play, and the betting market already prices it in.
How the humidor works
Coors Field sits about a mile above sea level, where the air is thinner and drier. Thin air means less drag, so a well-hit ball travels further. Dry air also dries out the baseballs, making them harder and bouncier. Since 2002 the Rockies have stored game balls in a humidity-controlled room, keeping them at the moisture level they would have at a normal park. A slightly moister ball leaves the bat a little slower. The humidor cannot change the thin air itself — only the ball. Since 2022 MLB has required humidors at all 30 parks.
What the data shows
Runs: +2.43 per game (95% CI 1.97 to 2.89, Welch t = 10.47, p < .001, a medium effect). Home runs: +0.25 per game (95% CI 0.09 to 0.41, t = 3.16, p = 0.002, a small effect). In other words, home runs explain only about a tenth of the extra runs. Coors has the biggest outfield in the majors, built that way because of the altitude, so more singles and doubles drop in and fielders cover more ground.
| Season | Games | Runs/game | HR/game | Avg closing total |
|---|---|---|---|---|
| 2021 | 81 | 10.65 | 2.49 | 10.91 |
| 2022 | 81 | 11.51 | 2.47 | 11.13 |
| 2023 | 81 | 11.84 | 2.57 | 11.72 |
| 2024 | 79 | 10.66 | 2.52 | 10.6 |
| 2025 | 81 | 11.72 | 2.68 | 10.99 |
| 2026 | 68 | 11.1 | 2.59 | 11.14 |
What it means for the total
The average closing total at Coors was 11.08, against 8.35 elsewhere — almost exactly the real scoring gap. Games went over 48.8% of the time (95% CI 44.3–53.4%), which is no different from a coin flip. "Coors means the over" is already in the number. Weather on the day — wind and temperature — still matters, so check the wind before first pitch.
How we measured this
Every regular-season game from 2021 to October 2026: 471 at Coors Field and 13,628 at other parks. Runs and home runs come from the MLB Stats API; closing totals are real closing lines, with pushes excluded. Differences use Welch's t-test, which does not assume equal variance. Past seasons before 2021 are not in our dataset, so this page does not measure the 2002 change itself.
Related
Where this is applied
These findings feed the game-time read on every MLB venue page, using the same sample-size and significance rules published here.
OverUnderWeather Research Desk
Independent data analysis on public sports and weather records. Studies match historical game outcomes to archived game-window weather, apply pre-set sample and significance rules, and publish null results when that is what the data show. Editorial policy and corrections log.
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Frequently asked
What does the Coors Field humidor do?
It stores game balls at a controlled humidity so they don't dry out in Denver's thin, dry air. A drier ball is harder and bouncier and flies further; a moister ball comes off the bat a little slower.
When did the Rockies start using a humidor?
In 2002. MLB then required humidors at every ballpark from the 2022 season, so every park now stores balls the same way.
Is Coors Field still the highest-scoring park?
Yes. From 2021 to 2026, Coors games averaged 11.25 total runs against 8.82 at every other park — 2.43 more per game (95% CI 1.97–2.89, p < .001).
Does Coors Field still give up lots of home runs?
Only slightly more than average: 2.55 per game against 2.3 elsewhere (+0.25, p = 0.002). Most of the extra scoring comes from hits falling in Coors' huge outfield, not from home runs.
Do Coors Field games go over the total?
No more than anywhere else. Bookmakers already price it in: the average closing total was 11.08, and games went over 48.8% of the time (95% CI 44.3–53.4%).