The volume of a round bar = Cross-sectional area x length of the bar

V = A x L

Let us consider a round bar of length 1m with a diameter of 20mm = 0.020m

So, the radius = 0.020/2 = 0.010m

Cross sectional area of round bar = A = πr^{2} = π x (0.010^{2}) = 0.0003142m^{2}

Density of mild steel = 7900 kg/m^{3}

Therefore, the mass of round bar = density x cross-sectional area x length of the rod

= 7900 x 0.0003142 x 1 = 2.4821 kg

Similarly, we can calculate the mass of the round bar of different dimensions.