In a string instrument, the scale length (often simply calle the "scale") is the sounding length of the strings. On instruments with strings which are not stopped (harp, piano) and on most fretless instruments it is the length of string between the nut and the bridge. On most modern fretted instruments the actual string length is a bit longer than the scale length, to provide some compensation for the sharping effect caused by the string being stretched a little as it is fretted. On such instruments it is not possible to determine the scale length by simply measuring the speaking length of the string.