Irish Acre

Seven thousand eight hundred and forty square yards, being the acre as reckoned on the Irish perch of seven yards.

An Irish acre is a little over one and three fifths of an English one, and for the same reason the Irish mile is long: it is built on a perch of seven yards rather than five and a half. The proportions within the system are identical to the English — forty square perches to a rood, four roods to the acre — so the whole structure simply scales up. The consequence for anyone reading Irish land records is considerable. A holding of a hundred acres in Irish measure is a hundred and sixty-two in English, and nineteenth-century documents frequently specify plantation measure or statute measure precisely because the difference was large enough to matter in rent, in tax and in inheritance. The Irish acre was also known as the plantation acre, after the seventeenth-century plantations during which it was widely applied to surveyed land.