A low value of deformation before crushing is an obvious and understandable measure of brittleness of materials including tablets. In this article, three methods based on deformation measurement in a flexure tester are compared. The simplest one is a plain measurement of distance from contact or selected start point till fracture. Next the brittle-ductile method (BDI), where the distance is established by normalisation of the force–displacement curve based on the work of failure (WOF). The third method is the tablet brittleness index (TBI) by Gong and Sun, where the reciprocal of a linear distance is proposed as a brittleness quantity. The study is based on data from a previous investigation, where tablets of microcrystalline cellulose and lactose in different combinations and with four different crushing forces were utilised. The investigation shows that the BDI method is preferable. It is easy to compute without data manipulation, the sensitivity to the fracture force is negligible and it provides an independent characteristic of the brittleness of a compacted material.