A
furlong is a measure of
distance in
imperial units and
U.S. customary units equal to one-eighth of a
mile, equivalent to 660
feet, 220
yards, 40
rods, or 10
chains. Using the international definition of the
inch as exactly 25.4
millimetres, one furlong is 201.168
metres. However, the
United States does not uniformly use this conversion ratio. Older ratios are in use for surveying purposes in some states, leading to variations in the length of the furlong of about two parts per million, or 0.4 millimetres ( inch). This variation is too small to have many practical consequences. Five furlongs are about 1.0
kilometre (1.00584 km is the exact value, according to the international conversion).