What is the official diameter of a modern table tennis ball?
Answer
40 millimetres
The official diameter of a modern table tennis ball is 40 millimetres.
The International Table Tennis Federation adopted the larger 40-millimetre ball for international play in 2000. Before that change, regulation balls measured 38 millimetres across. The increase was intended to make rallies easier to follow and to slightly reduce speed and spin.
Modern competition balls are hollow and usually made from plastic, although older regulation balls were made from celluloid. They must also weigh 2.7 grams and be spherical, with strict limits on how much they may vary in bounce and roundness.
The 40-millimetre measurement refers to diameter, not circumference. It is also separate from the ball’s color: approved balls are white or orange and must provide a clear contrast with the playing surface. The 2000 change is why older books and equipment guides may list 38 millimetres.