Why weight of steel bar is D2/162

Since we know weight of a steel bar per meter length in kg is
W = D²/162
Where W is the weight of steel bar and D is the dia of bar
Cross sectional area of steel bar
= ∏r²
[D=2r , r=D/2]
= ∏D²/4
Vol of steel bar per meter length
= ∏D²/4  x 1000
Density of steel
= 7850 kg/m³
= 7850 kg/1000 x 1000 x 1000
Now weight of bar per meter
= vol of steel bar x Density of steel
= ∏D²/4  x 1000 x 7850 kg/1000 x 1000 x 1000
= 3.14 D²/4 x 7850 x 1000 x 1000
= 0.785 D² x 0.007850
= 0.00616225 x D²
= 0.00616225 / 1 x D² / 1
= D²/1/0.00616225
= D²/162.28

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