To avoid the need for rolling-up excess length, using an extension reel or for cutting the cord to size, extension cords are sold in prefabricated lengths of 1 to 150 feet (30 cm to 45 m). Every foot of cord increases the electrical resistance, in turn decreasing the power the cord can deliver. Therefore, the longer the cord, the larger the diameter of the conductors need be to minimise voltage drop (wire gauge numbers are smaller for larger diameter wire). Because of this, it is best to use a cord that's exactly as long as needed and no more.