The document specifies a method to measure the length of adhesive tape on a roll. For non extensible adhesive tapes the length measured by this method shall be the same as the length after unrolling. For extensible adhesive tapes the length after unrolling shall be greater if the adhesive tape is stretched irreversibly by unrolling. It is also possible for an extensible adhesive tape to measure less after unrolling if stress built manufacture recovers after unrolling. This is important for all adhesive tapes with elongation at break of 80 % or greater.