Acre (ac)
Modern equivalent
4,046.86 square metres
Historically the amount of land a team of eight oxen could plough in one day. Approx. 4,840 square yards. Still used in the UK for land measurement.
Originally rooted in medieval agricultural practices, the acre represented what a yoke of oxen could plough in a single working day. Over time, it was standardised under various English monarchs, eventually becoming a statute acre in the 19th century.