Measurement trap
42.67 mm isn’t “the diameter of a golf ball.”
It’s the minimum permitted diameter under the rules.
Regulatory limit
Why this is interesting
It is one of the most quoted numbers in golf, and it is almost always quoted as the wrong kind of number.
How this measurement works
42.67 mm (1.680 in) is the smallest diameter a ball is permitted to have under the rules of golf. The rules set a floor, not a specification: a conforming ball must not be smaller than that, and manufacturers are free to make balls at or above it. So 42.67 mm describes the boundary of what is allowed, not the measured diameter of the ball in your pocket.
How certain is this?
Regulatory limit — a minimum permitted diameter, not a typical or universal measured value.
A rules floor, not a measured typical value.
Keep going
- What's the top of a mountain?Denali's official 20,310-ft elevation was measured to the top of its ice cap.
- How tall is a mountain, really?Mauna Kea is about 4.2 km above sea level — but nearly 10.2 km from ocean-floor base to summit.
- Where does a volcano begin?Mauna Loa is about 4.17 km above sea level — but about 17 km from its geological base to summit.
- Ball mathA regulation table-tennis ball is 40 mm in diameter and weighs 2.7 grams.
- Stack it upAbout 1,045.
- Stack it upAbout 110,000 quarters stacked flat would reach the top of the Gateway Arch.