The table tennis ball’s standard diameter increased from 38 millimetres to 40 millimetres in 2000.
The International Table Tennis Federation introduced the larger ball in 2000. The change followed a decision to make rallies easier to see and, in general, to slow the game slightly by increasing the ball’s air resistance. The older ball measured 38 mm, while the new standard measured 40 mm.
The rule change affected speed, spin, and timing. Players and manufacturers had to adapt their techniques and equipment, although the new ball remained the same nominal weight of 2.7 grams. The larger ball should not be confused with the later move away from celluloid toward plastic materials, which became significant from 2014.
Modern rules specify a ball with a diameter of 40 mm and a weight of 2.7 g. Those measurements are separate from the ball’s permitted white or orange color.