A denier is a unit of weight for fibres. It is defined as the weight of 9,000 meters of the fibre, and it is generally measured in grams. The current denier standard is 10 grams per 9,000 meters. Microns, also called micrometers, are units of measurement that equal one millionth of a meter. To put that into perspective, the diameter of a strand of human hair is between 20 and 180 microns. You can determine the diameter of a fibre in microns if you know its denier and density.
Convert the density of the fibre into grams per millileter (g/ml). For example, Fiber X has a density of 1.5kg per litre, or 1.5g/ml.
Divide the denier of the fibre by the density of the fibre. For example, Fiber X has a known denier of 2. The denier divided by 1.5 equals 1.333.
Take the square root of that number. In the case of Fiber X, the square root is 1.155.
Multiply the square root by 11.89. This will give you the diameter in microns. The diameter of Fiber X is 13.73 microns.