Electrospinning is remarkably a simple and versatile method for producing nanofibres. The diameter of nanofibres can vary from 10 nm to > 1000 nm. In electrospinning, most of the attention is focused on producing fibres with a uniform diameter. It is very important to understand how the diameter and its distribution vary with the materials used and the processing parameters. An analysis of literature sources has shown that the distribution curves of the diameters obtained are very complex and do not resemble normal distributions, while they do more closely correspond to those of compound distributions. The goal of this article is to analyse the distributions of the nanofibre diameters and to propose a new method for the evaluation process of nanofibres and the quality of a nanofibre web. The uniformity of structure and the quality of nanofibres web must be described by average values. The peaks of modal values and the percentage quantity of them must be used for evaluation of a web structure.