Furlong

What the unit was used for

The name is a description: Old English furh, a furrow, plus lang, long, the length of a furrow in a ploughed open field.

In the open-field system the arable was cut into long narrow strips, and an acre strip was conventionally a furlong long and a chain wide, which is why the acre is a thin rectangle and not a square.

What is well attested is why furrows were long: turning a team pulling a heavy plough was slow and awkward, so a furrow ran as far as the land allowed.

The furlong is the one unit of this group in daily British use, as the standard subdivision of a horse race.

In the system

1 furlong = 220 yards = 10 chains = 40 rods = one eighth of a mile

A story you will often hear

The furlong is commonly explained as the distance a team of oxen could plough without resting.

What the evidence shows: No scholarly source establishes it. Work on medieval land measurement points the other way: the standard furlong looks like a legal construct imposed on a very variable practice rather than a recorded fact of farming.