Chains and Acres

You learn something every day. After years of wondering how the acre came about as a measurement of area, here comes the Chain (length) (Wikipedia) to explain everything. An acre is apparently not just an inscrutably long and decimal-place–laden number of square yards. It is, in fact, exactly 10 square chains. A chain is one tenth of a furlong and equal to 66 feet. That makes more sense than 4840 square yards or a box 208.71 feet on a side.

In addition to the chain, there’s also the rood, which is a quarter of an acre, the perch, which is 1/160 of an acre (and equal to a square rod, which is 5.5 yards long) and the indian cent, which is 1/100 of an acre (but whose measurement in square feet or square yards is doubtless also fraught with decimal places).

So an acre is 10 square chains—a strip of land one furlong long and one chain wide, instead of a square of land—and a square chain is 1000 square links. It’s comforting to know that even the British system of measurement has roots in base-10.