<p>In work of structural strengthening, Fiber-reinforced polymer composites are becoming broadly necessary on account of their ease of application, affordability and for upgrading performance of both existing structures and structural components of various sizes. The lateral deformation of any composite strengthened compression member is predominantly affected for different sizes of members in existing structure. A precise assessment of structural behavior of the compression members for variable sizes during process of strengthening is constructive to achieve targeted strength as well as ductility of structural element. A lack of work as guidelines are available on columns for variable sizes to envisage the overall performance of RC columns after strengthening. To bridge this gap, the effect of size on the axial performance of carbon fiber reinforced polymer (CFRP) wrapped reinforced concrete (RC) columns has been mainly taken into account and tested all column specimens by controlling CFRP volumetric ratio and steel percentage as constant. A total of eighteen wrapped and unwrapped RC circular columns in three different diameters were tested for incremental axial compressive loading till it failed at ultimate load and the failure mode of different sizes of columns were analysed. The test outcomes explicitly revealed that size variation has an impact not only on the strength and ductility but also internal steel reinforcements, composite wrap and concrete behaviour of confined RC columns. Stress–strain behavior exposed that as column size increased, the values of yield and ultimate strength for wrapped also unconfined columns decreased. The variation in size of columns is also influenced on strain contribution of internal reinforcement, concrete and CFRP confinement in process of strengthening. The observed behavior of confined columns with variation in sizes is remarkable to predict the efficiency of confinement and its effects while process of strengthening of columns.</p>