Physics and Acoustics of Baseball & Softball Bats Daniel A. Russell, Ph.D. Graduate Program in Acoustics The Pennsylvania State University The contents of this page are ©2003-2011 Daniel A. Russell

# How are Baseball and Softball Bats Different?

What are the differences between a softball bat and a baseball bat? Why can't you (or should't you) use a softball bat to play baseball, or a baseball bat to play softball? How do youth baseball bats compare to adult baseball bats and/or slow-pitch softball bats?

At the youth level (Little League Baseball and Softball) there is no distinction between a baseball bat and a softball bat. A 30-inch youth bat is the same regardless of which sport it is used for. However, at the adult level noticeable and important differences between softball and baseball bats exist. As I will try to demonstrate on this page, adult baseball and softball bats are quite different. And, even for softball bats there are significant differences between bats used for slow-pitch and fast-pitch games.

## Bat Length and Weight

The most obvious difference between youth bats, softball bats, and baseball bats is length. The photo at right shows the differences in length for the same make and model bat (Demarini Vexxum) as used for (from left to right) adult baseball, adult slow-pitch softball, and youth baseball/softball. While it is true that each type of bat is available in a variety of lengths, the bats in the photo represent the most common lengths for each type. The table at right summarizes the range of lengths and the most commonly used length for each type of bat (baseball - 33", softball 34", youth - 30").

Another significant difference between youth, softball and baseball bats is the bat weight. The table at right shows the range of weights for each type of bat. The primary reason for the range of available weights is that the speed with which a player can swing a bat is somewhat related to weight, though bat swing speed is more strongly dependent on moment-of-inertia which is directly linked to the weight and length of a bat. Little League youth bats are the lightest, and have the greatest range of available weights, with composite and aluminum bats weighing much less than wood bats. For adult slow-pitch bats the most popular weight is 28oz. However, variations in the distribution of mass (and the location of the balance point) can make the apparent swing weight of 28oz bat feel much ligher or much heavier than its actual weight. Many older slow-pitch softball bats from the 1970's and 1980's were much heavier, weighing in between 34-38oz. Fast-pitch softball bats are generally lighter than slow-pitch softball bats, because the higher speed of the pitched ball means that the batter has less time to decide to commit to swing and must be able to swing the bat faster.

The range of weights for adult baseball bats (which bear the BESR certification mark required for High School and NCAA college play) is much smaller because of the "minus-three" rule. One of the restrictions on bats, imposed by the NCAA to lower the performance of aluminum bats, is that the numerical value of the weight in ounces must be no more than three less than the numerical value of the length in inches. So, a 33" baseball bat could have weights of 33oz, 32oz, 31oz, and 30oz, but not 29oz. In major league baseball, where players use only wood bats, the weight of the bat is only limited by the requirement that the bat be made entirely out of solid wood, and by the fact that the handle of the bat breaks if it is made too thin. Most major league players use bats that weigh 32-34 ounces. But, some of baseball's greatest players (like Babe Ruth, Ty Cobb, Joe DiMaggio) used bats as heavy as 42oz.

Bat TypeLength Range
Youth (Little League) 29" to 32"
Adult Slow-Pitch Softball 33" to 34"
Fast-Pitch Softball 32" to 34"
Bat TypeWeight Range
Youth (Little League) 14oz to 27oz
Adult Slow-Pitch Softball 26oz to 30oz
Fast-Pitch Softball 23oz to 28oz
(minus 3 rule)

Same make bat (DeMarini Vexxum) offered in various models for use in adult baseball model (33" 30oz), slow-pitch softball (34" 28oz), and youth baseball (30" 20oz).

## Bat Profiles (Barrel Diameter)

Barrel Diameter After differences in length, the second most obvious difference is that the barrels of baseball bats are fatter than those of softball bats. The barrels of adult baseball bats, which are used for play under NCAA college and high school rules, are 2-5/8" in diameter. This is a relatively recent reduction in diameter from 2-3/4" prior to 1998 when NCAA began implementing size, weight, and performance limits on bats. Adult softball bats (both slow- and fast-pitch) are narrower, with diameters of only 2-1/4". Youth bats have the same diameter as adult slow-pitch bats. In fact, 30" youth bats offered by several manufacturers are simply 34" adult slow-pitch bats with two inches cut from both the handle and barrel ends.

Bat TypeBarrel Diameter
Youth (Little League) 2-1/4"

Diameter versus Length Profiles More noticeable, however, are differences in the way in which the diameter varies along the length of the bat. The profile of composite and aluminum softball bats and youth bats can be separated into three well defined regions: barrel, taper, and handle. The thin handle (usually about 12" long for softball bats) has a constant width over its entire length. The thin handle is joined to the wider barrel with a smoothly increasing diameter taper region (usually about 6" long for softball bats). The barrel has a constant 2-1/4" diameter over its entire length (12-14" for softball and 8-10" for youth). Fast-pitch bats often have a barrel that takes up almost half the length of the bat. These "bottle bats" have a very short taper region and are designed to provide a larger hitting area and to allow a hitter to make better contact with the ball for inside pitches.
Adult baseball bats also have a long handle of constant width -- but the handle diameter is slightly larger than that of a softball bat. The constant diameter region of the barrel (if there is one) is much shorter, at most 6-inches, and the taper region over which the diameter increases from handle to maximum barrel diameter is much longer. In fact, some adult baseball bats don't have a constant diameter barrel at all but are pretty much just one long taper reaching a maximum diameter a couple of inches from the end of the barrel.
Wood bats have slightly different profiles than metal or composite bats. The handles are thicker - to add strength so they break less often - and the handle diameter flares out at the know instead of maintening a constant width. With the exception of some "bottle bat" designs (see photo) most wood bats don't have a well defined barrel region with constant diameter. Even youth and softball bats tend to have a gradual taper from the thinner handle to a maximum diameter a couple of inches from the barrel end, and the barrel end of the bat is much more rounded than composite or metal bats.

Adult Baseball Bat (top) and Adult Slow-pitch Softball Bat (bottom). The baseball bat is 1-inch shorter, but has a larger diameter barrel than the softball bat.

Same make bat in youth (top), softball (middle) and adult baseball (bottom) models. Barrel diameters for the youth and softball bats are the same, and the adult baseball bat is wider.

Aluminum youth baseball, adult slow-pitch softball, adult fast-pitch softball bats. Barrel diameters are the same for all three bats, but the diameter versus length profiles are noticeably different.

Diamter-length profiles for 34" composite slow-pitch softball and aluminum adult baseball bats.

Differences in diameter versus length profiles are even evident when comparing Wood youth baseball, adult slow-pitch softball, and adult baseball bats.

## Barrel Stiffness (Trampoline Effect)

There are also differences between youth, softball and baseball bats in the effective stiffness of the barrel. This is primarily due to differences in the elastic properties of baseballs and softballs. A hundred years ago, the games of "hardball" and "softball" lived up to their names in terms of the balls that were used for each game. Modern softballs are definitely not "soft" and depending on whether you are measuring static or dynamic stiffness, can actually be harder than baseballs. Besides having different weights and diameters, baseballs and softballs differ considerably in construction and elastic properties. A typical baseball has a coefficient-of-restitution (COR) of 0.55, which means that when thrown against a hard surface it will bounce back with a little more than half of its original speed. Softballs come in a variety of COR values, most being either 0.40, 0.44, or 0.47. Essentially, the COR value specifies how much energy is lost due to internal friction as the ball deforms during impact. In addition, softballs come in a variety of compression values (force in pounds necessary to squish the ball a quarter of an inch), usually 525-lbs, 375-lbs, or 150-lbs (safety balls). Furthermore, the pitched ball speeds are different between baseball and softball. In baseball, pitched ball speeds are usually well above 80mph, reaching 90-95mph at the professional level. In slow-pitch softball pitched ball speeds are much lower, around 25mph. Fast-pitch softball is much faster, with speeds actually pretty close to those in baseball. The difference in ball speeds couples with the differences in elastic properties of the ball to make for differences in the interaction with a bat.

The trampoline effect is the result of the barrel of a hollow bat squishing during the impact with the ball. The bat barrel essentially acts as a spring, storing some of the energy which would otherwise have gone into compressing the ball and been lost to internal friction forces. As the bat barrel expands it returns most of its stored energy to the ball and the resulting ball speed can be significantly higher than it would have been for a wood bat which does not have a trampoline effect. The effectiveness of the trampoline effect and the bat-ball collision depends on both the elastic properties of the bat and ball. Since the elastic properties of baseballs and softballs are considerably different, the elastic properties (the spring-like behavior of the barrel) has to be different for baseball and softball bats in order to optimize the trampoline effect. Elsewhere on my website I will discuss the physics behind the trampoline effect in greater detail. But it will suffice to say here that the barrel stiffnesses of a high performance baseball bat and a high performance softball are significantly different, with the barrels of baseball bats tending to be stiffer than softball bats. In my laboratory I measure barrel stiffness in terms of the hoop frequency and have found that higher performance bats have lower hoop frequencies.[1] A high performance softball bat will have a hoop frequency around 1200 Hz, with most ASA approved softball bats having hoop frequencies above 1500 Hz. An NCAA approved high performance adult baseball bat will have a higher hoop frequency somewhere around 1600 Hz, and hoop frequencies for most current baseball bats are above 1800 Hz. Youth bats have similar hoop frequencies as adult baseball bats. This may be a surprise since the youth bat barrels have the same diameter as softball bats. However, the barrel of a youth bat is several inches shorter than a softball bat, and the shorter barrel length results in a higher hoop frequency, or higher barrel stiffness.

## Matching the Right Bat to the Right Game

At the youth level there is no difference in bats for softball and baseball. The dynamics of the game at the youth level are quite different than when played by adults who are stronger and more experienced. But, at the adult level, baseball and softball bats are designed to match their respective games. Conceivibly you could use a baseball bat to play softball, as long as you can adjust to the slightly shorter total length, and the heavier weight. You would probably find that the performance would be about the same as an older lower performance softball bat. Using a softball bat to play baseball would most likely result in cracking or breaking your bat. Softball bats are not designed to withstand the forces resulting from an impact with a baseball. The performance might be really good and the ball might come off the bat pretty fast, but you would most likely break your softball bat. The same would be true of using a fast-pitch softball bat in a slow-pitch game; you would probably damage your fast-pitch bat. You could use a slow-pitch bat in a fast-pitch softball game without damaging it but the larger weight (actually, larger moment-of-inertia) makes the slow-pitch bat more difficult to swing quickly and you would probably not hit as well.

References

[1] D.A. Russell, "Hoop frequency as a predictor of performance for softball bats," Engineering of Sport 5, Vol. 2, pp. 641-647 (International Sports Engineering Association, 2004). [author's preprint version (PDF)]

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