Where is the formula D²L/162 came from?


The formula is D²L/162


D = Diameter of steel bar in millimetre

L = Length of steel bars in meter


We know that,

Weight= Cross sectional area x Length x Density

For steel bar, this also remains same.

The weight of steel bars= Cross sectional area of steel bar x Length of steel bar x Density of steel bar.

That means,

W = A x L x ρ


W = Weight of steel bars

A = Area = πD²/4

π (pi) = 3.14

D = Diameter of steel bar in millimeter

L = Length of steel bar in meter

ρ (Rho) = Density of steel bar = 7850 kg/m³


W = 3.14 x D²/4  x L x 7850

But there is two conflicting unit in the formula. Which is millimetre for D and meter for ρ (Rho).

So we need to convert either D or ρ to the same unit.

Let’s change the unit of D from millimetre to meter.

1 millimetre = 0.001 meter

Let’s put this into the formula,

W= 3.14 x {(D² x 0.001 x 0.001)/4} x L x 7850

= D²L/162




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