As the Laws were formulated in England, and were initially administered solely by the four British football associations within IFAB, the standard dimensions of a football pitch were originally expressed in imperial units. The Laws now express dimensions with approximate metric equivalents (followed by traditional units in brackets), though use of imperial units remains popular in English-speaking countries with a relatively recent history of metrication (or only partial metrication), such as Britain.

Imperial units where once used to express the dimensions of a what?