How Air Density Impacts MLB Baseball Games

Coors Field Affected By Air Density

Everyone knows that a baseball travels farther at Coors Field because of the thin air, right? But what exactly does that mean? And what forces are at play? Simply stated, there are two basic forces that drive this effect…air resistance and magnus force. And, interestingly enough these factors are at play in other ballparks as well. In fact, they impact games in all non-dome ballparks to some degree.

Air resistance, also known as drag force, is the force that acts upon the baseball as it cuts through the air…the denser the air, the more resistance on the ball. In a vacuum (no air resistance), a baseball would travel approximately twice as far as it does through normal air at sea level. However, in the real world, average air density causes a pitched ball to lose approximately 10% of its velocity by the time it crosses the plate. Thus, it comes as no shock, that a baseball, whether batted or pitched, will travel further and faster in lower air density conditions.

Magnus force is the force that causes a spinning baseball to curve or “break”. The impact of air density on Magnus force is more or less proportional to the measured air density. A drop in air density of 10% will result in a proportional 10% less ball movement. Thus, pitchers that rely more heavily on ball movement in lieu of good velocity on their fastball may be more likely to struggle in lower air density. Julio Tehran (ATL), Adam Wainwright (STL), and Luke Weaver (ARI) come to mind.

Factors that affect air density, and thus air resistance and magnus force, include altitude, temperature, and humidity. However, it is altitude that is most impactful. At an altitude of 5,200 ft above sea level, Coors Fields in Denver, CO has an average game time air density of .79 (79% that of sea level), by far the lowest average air density in MLB. Yet, other parks can experience low air density as well (Chase Field routinely drops below .83, and Globe Life Park in Arlington hit .83 in July 2018). This less dense air causes flyballs to travel farther (more homeruns), fastballs to be faster, and breaking balls to break less (more hard hit balls). On the flip-side, when air density approaches 1.00 at Comerica Park in Detroit (avg. game time air density on .94), the number of homeruns decreases dramatically (420ft to dead center field).

Rules of Thumb: How Air Density impacts MLB baseball games

  • Batted balls travel ~1 ft further/shorter for every 1% change in air density. So, on average a flyball in Denver travels ~18 ft further than one in Oakland.
  • Breaking balls (or any pitch that relies on movement) move proportionally less is low air density. So, on average, a pitch that has six inches of movement in Oakland will display only 4.8 inches of movement in Denver.
  • Pitches gain ~1mph in velocity with a 20% drop in air density.

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