Fracture in concrete structures is generally accompanied by progressive cracking. This process is very complex and can be identified by associated crack parameters such as crack openings and crack length. These parameters are the direct indicators of the local failure in the material microstructure and can completely describe the fracture process of the concrete structure. The purpose of this article is to monitor experimentally the crack openings in geometrically similar concrete beams with different sizes. An experimental approach is used to estimate the effective crack length from the crack opening profile. For this, the digital image correlation technique is applied on the specimen surface to capture crack propagation. Size effect on the crack propagation is also investigated.