What Is Park Factor and How It Affects Home Runs

Park factor is a number that measures how much a ballpark inflates or deflates an outcome, like runs or home runs, compared to a league-average park. It is scaled so 100 is neutral: a mark above 100 means the park boosts that outcome, and below 100 means it suppresses it. Coors Field in Denver is the most extreme, well above 100 for run scoring.

How park factor is calculated

A park factor compares what happens inside one ballpark to what the same players do everywhere else. Statcast builds its version by taking each batter and pitcher, controlling for handedness, and comparing how often a given outcome occurs in that park versus those same players' results in other parks. The result is put on a scale where 100 is exactly average. A home run park factor of 115 means that park produces about 15 percent more home runs than a neutral park, and a mark of 90 means about 10 percent fewer.

To smooth out year-to-year noise from weather and small samples, park factors are usually calculated over a multi-year rolling window rather than a single season. A one-year number bounces around too much to trust.

Why parks are not equal

Several physical features push a park above or below 100:

• Dimensions and wall height. A short fence is easier to clear. A deep gap or a tall wall like Fenway's Green Monster turns some home runs into doubles or outs.
• Altitude and air. Thin air lets the ball carry farther. Coors Field sits about a mile above sea level, which adds meaningful carry to well-hit fly balls and is the main reason it is baseball's top run-scoring park. Over the 2023 to 2025 window its run index sat around 128, roughly 28 percent more runs than an average park.
• Temperature and climate. Warm air is thinner, so hot-weather and open-air parks tend to play bigger than cold or marine climates.
• Foul territory. Large foul ground turns more fouls into outs, which quietly suppresses offense.

Handedness makes it asymmetric

A single park often plays very differently for left-handed and right-handed hitters, which is why a good park factor is split by handedness. Yankee Stadium is the classic example: its short right-field porch inflates home runs for left-handed pull hitters while playing close to neutral, or even below, for righties. Treating a park as one number for everyone hides the edge. A lefty slugger in a park with a short porch on his pull side is a very different bet from a righty in the same building.

How to use park factor for home run bets

Park factor is a multiplier on top of a hitter's own power, not a stand-alone reason to bet. A power hitter in a hitter-friendly park, on the side of the field the park favors, has a real tailwind. The same hitter in a pitcher's park loses some of that edge. It works best read together with the pitcher matchup and the weather, because a favorable park can be canceled out by wind blowing in, and a neutral park can play big on a hot day with the wind out.

How BetLogic helps

BetLogic's HR Sheet applies a handedness-aware, asymmetric park factor as one input when ranking the day's home run plays, then layers in the pitcher, weather, and recent power. For the contact stat underneath a home run, read what barrel rate is, or start with how to bet MLB home run props.

BetLogic provides data-driven insights only and does not constitute financial or gambling advice. Please bet responsibly and only what you can afford to lose. You must be of legal betting age in your jurisdiction.