How Much Does a Baseball Weigh? Official Size by Level

A regulation baseball weighs 5 to 5.25 ounces — 142 to 149 grams, or about a third of a pound. It measures 9 to 9.25 inches around, which works out to a diameter of roughly 2.9 inches.

That's the short answer. But the question "how much does a baseball weigh" has a stranger answer underneath it. The rule gives a range instead of a number. Not every level of play uses the same range. And college baseball allows a ball that is legally bigger than anything Major League Baseball would put on the field.

The Official Spec Is Rule 3.01

The number traces to one sentence in the Official Baseball Rules:

"It shall weigh not less than five nor more than 5¼ ounces avoirdupois and measure not less than nine nor more than 9¼ inches in circumference."

One correction worth making, because a lot of articles get it wrong: this is Rule 3.01, not Rule 1.09. MLB renumbered its rulebook in 2015. Sources still citing 1.09 are quoting a decade-old edition. It gets confusing because Little League's ball rule genuinely is numbered 1.09 — different rulebook, same digits.

In every unit you might need:

If you need one number for a physics problem, use the midpoint: 5.125 oz, or about 145 grams.

Baseball Size and Weight by Level

Here is where the common assumption breaks. Weight is genuinely identical everywhere — every organization below uses 5 to 5.25 ounces. It is the circumference that moves.

The NCAA line is not a typo. The NCAA Baseball Rules Book sets the ceiling at nine and a half inches — a quarter inch more than the pros allow. Nearly every article on this topic states that college and MLB balls share a spec. They don't.

USSSA runs the other direction, permitting a ball down to 8.95 inches. So the full legal span across American baseball is 8.95 to 9.5 inches, not the 9 to 9.25 everyone quotes.

Why the Rule Gives a Range at All

Manufacturing tolerance. A baseball is wool, cotton and leather wound by machine and stitched by hand, and organic materials don't come out identical. Read the spec the way a factory would: 9.125 inches ± 0.125, and 5.125 ounces ± 0.125.

A quarter inch sounds academic until someone measures it. A collector did exactly that with two game-used balls from Wrigley Field in 2022 and photographed them side by side. One came in at 9.00 inches, the other at 9.25 — the legal floor and the legal ceiling, both from the same season. The difference is visible in the photo.

That reframes a familiar sight. When a pitcher waves off a brand-new ball, most fans assume it's about feel or scuffing. Some of it is size — a variable almost nobody thinks about.

What's Actually Inside

Weight is not distributed the way most people guess. The cork-and-rubber core, called the pill, is smaller than a golf ball at about 4.25 inches around. It accounts for a small share of the total. The bulk of a baseball's mass is yarn — four separate windings of wool and a poly-wool blend, layered over the pill.

The wound center is weighed and measured before the leather ever goes on, and it already measures close to nine inches around. The cowhide cover and its 108 hand-sewn stitches add very little size, and only about an ounce of weight.

Counting drying cycles, one professional ball takes about a week to build.

Humidity Changes the Weight

Wool and leather absorb water, so a ball's weight is not fixed once it leaves the factory. Physicists at the University of Colorado measured this directly: moving balls from 30% to 50% relative humidity made them 1.6% heavier and 0.24% larger. Testing across a wider humidity range at Washington State's sports science lab pushed the weight gain to 7.4%.

A wetter ball is heavier and less lively, and it leaves the bat slower. This is why every MLB club has stored balls in a humidor since 2022 — 70°F and 57% relative humidity, with Coors Field set higher at 65%. The point isn't to deaden offense. It's to stop the ball from being a different object in Denver in July than it is in Miami in April.

For anyone storing team balls at home: a damp garage will quietly put your practice balls outside spec.

How to Read the Stamp on the Ball

Since weight and size are nearly identical across levels, the printing on the leather is what actually tells you whether a ball is legal for your league.

• NOCSAE mark — required on every high school ball since 2019 under NFHS Rule 1-3-1.
• RS or RS-T — Little League licensing. RS is regular season only; RS-T is also approved for tournament play.
• USSSA mark — required for USSSA sanctioned play, alongside the compression standard.

One high school coach describes feeling a bad seam while throwing a foul ball back, checking the print, and finding a 12U ball bought at a big-box store had been mixed into a tournament. The umpire pulled the whole batch. The ball weighed the right amount and was the right size — it simply wasn't a legal ball.

Youth balls also differ inside. Lower-level balls often use cork or a cork-yarn blend with looser winding, while higher-level balls use a rubber center and denser yarn. Same numbers on paper, different ball in the hand — a distinction worth knowing whether you're buying by the dozen or setting up a camera behind the plate.

Baseball vs Other Balls

A cricket ball is the close relative here — slightly heavier than a baseball and slightly smaller around. A softball is neither small nor soft, running roughly 30% heavier.

The Short Version

A baseball weighs 5 to 5.25 ounces and measures 9 to 9.25 inches around, per Rule 3.01. That weight holds at every level of American baseball. What changes is circumference — NCAA balls may legally reach 9.5 inches, USSSA balls may drop to 8.95 — plus the certification marks that decide whether a ball is legal where you play. The range in the rule is real enough to see with your own eyes, and humidity moves a ball within it long after it leaves the factory. If you only remember one number, make it 145 grams.