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).