Intumescent coatings employ the heat barrier effect of an expanded char in the fire protection of the underlying substrates. The effectiveness of an intumescent system is dependent on the strength and ability of the char to remain intact upon exposure to fire. Many approaches have been employed to measure the strength of the intumescent char, but there still remains the need for an established standard procedure. In the present study, the compressive strengths of reinforced and unreinforced intumescent chars are evaluated using the compression test for cellular materials (ASTM 1162 00). This standard procedure enabled easy evaluation of compressive strength by employing the principle of deformation force as a function of the axial displacement of char under an active load by using the common universal tensile testing machine. The force�deformation graph revealed an exponentially increasing curve with two distinct regions, an initial region of low force to high deformation representing the collapse of the cellular pores and a high-force�low-deformation region attributed to the bulk mass effect of the compressed char. The results showed that the force needed to compress a bauxite residue-reinforced char to 10 deformation increased by 59, while the compression strength increased by 13.08 over the control char. © 2021, American Coatings Association.