Centimeters or millimeters.
That depends on the length of staple used.
The part is the staple part is where the spring is
A ruler.
staple
A millimetre.
staple is an element of fiber, pertaining to the length of an individual fibrous hair. Staple length is useful to handspinners to know how finely to spin their wool based on the breed. Staple can vary between breeds of wool or other fiber, e.g. Merino commonly has a staple of 2-4 inches, while others may have very long staple length. To see for yourself, hold a small piece of fiber or roving from either end and gently pull outwards, until the fiber pulls appart. Measure one of the pieces, and that is your approximate staple length.
Yarns that are spun from short fibres, like cotton. The staple is the length of the fibre, so you might say 'Egyptian cotton is better quality than Indian cotton because it has a longer staple.' Many artificial yarns are extruded, that is made like squeezing toothpaste from a tube, so they don't need to be spun to make a long thread.
I would use vernier callipers.
Jute is classified as a staple fiber. This means that instead of being one continuous length (filament), jute fibers are short in length and are spun or twisted together to form yarns for weaving.
Staple
<p>UHML is the average length of the longest half of the fibre population by weight. Longer fibres account for more of the mass of the sample than do more numerous shorter fibres. Generally speaking, staple lengths are normally distributed when normalised by weight.<p>
Tencel is a staple fibre. That is it is cut into staple lengths during production so that it can be processed into yarns and nonwoven fabrics on conventional textile processing machinery. The cut lengths are similar in length to cotton or to wool. Continuous filament Tencel yarns are not produced but in theory could be. In a filament yarn all of the fibres in the yarn have the same length as the piece of yarn.