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 = πr2 = π x (0.0102) = 0.0003142m2
Density of mild steel = 7900 kg/m3
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.