As per IS 456 ∶ 2000, short axially loaded RC column members using mild steel are des by the equation
where,

P_u = factored axial load on the member

f_ck = characteristic compressive strength of the concrete

f_y = characteristic strength of the compression reinforcement

A_g = gross cross sectional area

A_c = area of concrete

A_sc = area of longitudinal reinforcement of column