The sizes used for Japanese pipes are based on the Whitworth pipe system but they are often labelled using millimetres. This page gives equivalents in Whitworth sizes and Japanese sizes.
|Millimetre pipe size||Whitworth/inch pipe size|
|13 mm||G 1/2||This is the standard pipe size used in most Japanese plumbing. G 1/2 is a type of Whitworth connector.|
|20 mm||G 3/4|