Probably D2/162 is the first formula we ever learn in the construction industry. We know it is used to calculate the weight of steel bars.

Also, know the importance of estimation in the Bar Bending Schedule. Here we are going to discuss the derivation of this formula.

different size steel rods

Derivation of D2/162 

We know, Weight = Area X Density

To find out the weight of steel,

Weight of steel per metre = Area of Steel X Density of Steel X Length of Steel

We know that 

So,

Weight of Steel per metre =  Area of Steel X Density of Steel X Length of Steel

= πD2/4 x 7850 x 1m

= 3.14 x (D2 / 4) x 7850 x 1m

When multiplying all values should have the same unit. Here diameter is in mm and unit weight is in m3.

1 mm = 1/1000 m ; 1 mm2 = 1/(1000)2 mm2

= 3.14 x (D2 / 4) x 1/(1000)2 x 7850

= D2 x 6162.5 x 1/(1000)2

= D2 X (0.006162)

= D2 X 1/(0.006162)-1

= D2/162.28

Weight of Steel per metre = D2/162.28

If you want to know the steel weight per foot. 1 metre = 3.281 ft. Just multiply the same.

Weight of steel per foot = D2/162.28 x 3.281 = D2 / 533

Happy Learning 🙂

Author

Satheesh is a Civil Engineer who has more than 9+ Years of experience in residential construction. He is the author, editor of Civil Planets

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