The word acre comes from an Old English word that meant open field. Originally, that was pretty literally what an acre was: an open field and the amount of it that an ox could plow one sunny day. 

An acre was considered to be a rectangle with one side that was one chain length and the other side that was one furlough length. Before measurements were more standardized, the size of an actual acre varied widely between different countries. Internationally, one acre is now considered to be equal to 4,046.8564224 square meters. 

Other types of acres include the builder’s acre and other regional acres. The builder’s acre is a measurement used in the United States for construction and real estate. One acre is equal to 40,000 square feet, which is about 10% smaller than an international acre. The number is used because it is even and makes calculations easier. 

Other countries also have their own varied measurements for an acre. For example, the Irish acre is 7,840 square yards and the Roman acre is 1,260 square meters. God’s acre isn’t a measurement at all, but a term for a churchyard.