Fibre length is a genetic trait, and varies considerably across different cotton species and varieties. Length and length distribution are also affected by agronomic and environmental factors during fibre development, and mechanical processes during harvesting and ginning. Length is of importance to the spinning industry as longer fibres allow finer and stronger yarns to be spun.

Length is measured on a sample of fibres, either by pulling a hand staple, or by the HVI™ machine by passing a beard of parallel fibres through an optical sensing point. Australian cotton is all classed using HVI™ measurements and is reported in 100ths and in 32nds of an inch. Under dryland conditions, staple length can vary from, irrigated cotton (1 1/8 inches) down to very short (1 inch or less). Australian base grade is 36 or (1 1/8”). Table 3 gives an indication of both 32nds and 100^th of an inch.