Abstract: Wherein the length of a flexible web or string material, such as a textile material, forming a wound body or roll (10) may be determined by determining a first measure of the weight of the web or string material, determining a second measure of the weight of a predetermined length (1) of the material, and calculating the total length of the flexible web or string material on the basis of said predetermined length (1) and said first and second weight measures. Thus, a roll (10) of a textile material may be placed on a table (12) divided into sections, of which a first section (11) supports the roll while a second section (14) supports the predetermined length (1) of the material. The second section and the web material arranged thereon may be supported by a weighing cell and the whole table (12) and the web material or textile material arranged thereon may be supported be another weighting cell.