How far a swimmer swims. Distances for short course are: 25 yards (1 length), 50 yards (2 lengths), 100 yards (4 lengths), 200 yards (8 lengths), 400 yards (16 lengths), 500 yards (20 lengths), 1000 yards (40 lengths), 1650 yards (66 lengths). Distances for long course are: 50 meters (1 length), 100 meters (2 lengths), 200 meters (4 lengths), 400 meters (8 lengths), 800 meters (16 lengths), 1500 meters (30 lengths).