If you mean the length of tartan used to make a man’s kilt, it is usually 7 to 8 yards long when all the pleats are unfolded, depending on the customers measurements.
If you mean how long a kilt should be when worn, then the band at the top should sit above the hips on the natural waist or a little higher. The bottom selvedge should be anywhere from the top to the middle of the kneecap. Slightly too short is always preferable to a kilt that is in any way too long.