Scaleidoscope

Measurement trap

A golf ball isn't required to be exactly 42.67 mm wide.

42.67 mm is the minimum permitted diameter

The rules say a ball must be not less than 1.680 in (42.67 mm) across. That's a limit, not the size of every ball.

Regulatory limit

Why this is interesting

It's one of golf's most quoted numbers, and it's usually quoted as the wrong kind of number.

This is the difference between a defined measurement and a permitted limit. A table-tennis ball is specified around a defined size. The golf-ball rule instead says the ball must not be smaller than a certain diameter. Those are different kinds of standards.

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.

Minimum does not mean exact

A conforming golf ball may be larger than 42.67 mm. “Minimum diameter = 42.67 mm” is the rule; “golf-ball diameter = 42.67 mm” is not.

Not too small. Not too heavy.

The same equipment rules also cap the ball's mass at 1.620 oz (45.93 g). Diameter gets a floor; mass gets a ceiling.

Diameter
not less than 1.680 in (42.67 mm)
minimum
Mass
not greater than 1.620 oz (45.93 g)
maximum

How certain is this?

Standardized regulatory limit. 42.67 mm (1.680 in) is the smallest diameter the rules allow — not a typical or universal measured size.

A rules floor, not a measured typical value.

Sources & further reading

Follow this rabbit hole

Ball mathA regulation table-tennis ball is exactly 40 mm across

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Back to the converterExplore the measurement library