How to calculate unit weight of steel bar

What is Steel?

Steel is the most versatile commonly used structural material. The essential elements in steel are metallic iron and the element non-metallic carbon, with small quantities of other elements such as silicon, nickel, manganese, chromium and copper. It is thus an alloy. Though steel is usually more than 90% iron, with other elements present in small quantities, these other elements have a pronounced effect on the properties of steel.

Types of Steel

Depending upon the chemical composition, different types of steels are classified as:

  1. Mild Steel
  2. Medium Carbon Steel
  3. High Carbon Steel.
  4. Low Alloy Steel
  5. High Alloy Steel

Out of these, the first three types of steels are known as structural steel, commonly used in steel structures. In Indian standard IS:800-1984(Code of practice for general construction in steel) is applicable to the types of structural steels covered by the following Indian Standard:

1. IS     :     226-1975 Structural Steel (Standard Quality)

2. IS     :     1977-1975 Structural Steel (Ordinary Quality)

3. IS     :     2062-1984 Weldable Structural Steel

4. IS     :     961-1975   Structural Steel (High Tensile)

5. IS     :     8500-1977 Weldable Structural Steel (medium and high strength qualities)

Steel conforming to IS: 226-1975 is suitable for all types of structures subjected to static, dynamic and cyclic loading, and is suitable for welding up to 20 mm thickness. The physical properties of mild steels are as under:

1. Density or Unit Weight of Steel –  7850 kg/m3

2. Youngs’s modulus of elasticity (E)  –  2.04 x 105 Mpa (or N/mm2)

3. Modulus of Rigidity (G)                  –  0.785 x 105 Mpa (or N/mm2)

4. Poisson’s Ratio(µ)                             –  0.3 (inelastic rang)

5. Coefficient of thermal expansion or contraction  –   12 x 10-6 per °C or 6.7 x 10-6 per °F

Also, read – Difference Between Mild steel and Stainless Steel

Calculation of Weight of steel bar for 1-metre Length

Weight = Density × Volume (Volume = Area x Length)

Example:-  Diameter of Bar = 10 mm and Length = 1 metre

Area of circular bar = π/4 × d2

                                  = 3.14/4 × 102

                                  =   78.5 mm       

Volume      =   Area × Length

                  =    78.5 × 1000                  (1 metre = 1000 mm)

                  =    78500 mm3

Unit Weight of steel bar for 10 mm    =   (7850/1000 ×1000 ×1000) × 78500    

                              =  0.616 kg/m               (1 kg/m3 = 0.000000001 kg/ mm3)


Similarly, we can calculate the unit weight of the square and rectangular bar.

Derivation of Formula for Calculating Unit Weight of Steel

As we know the density of steel  =  7850 kg/ m3

Weight of steel per metre     =  Volume × Density [ Volume = Area × Length ]

=  π/4 x d2 × 1000 × 7850 kg/m  (length = 1000 mm)  

=  0.785 × d2 × 1000 × 7850 kg / (1000 × 1000  × 1000) [ 1 metre = 1000 mm ]

=  785 x d2 × 0.00000785

=    d2/1  ×  0.00616225 /1

=    d2/1/0.00616225

=    d2/162.27 ≈

=     d2/162   kg/m     (say)

Unit Weight of steel bar per feet    =  d2/(162.27 x 3.28084)         (  1 metre = 3.28084 feet)

                                            =   d2/532.38 ≈

                                            =   d2/533 (say) 

                                            =  d2/533  kg/feet

Unit Weight of Steel Bars Per Metre Length

S.No.Dia of Bar Weight of Bar Per Metre Length(D2/162)
18        0.395
210        0.619
312        0.888
416         1.58
520         2.469
625         1.388
728         4.839
832         6.32
940          9.87

Unit Weight of  Steel Bar Per Feet Length

S.No.Dia of Bar Weight of Bar Per Metre Length(D2/533)
18              0.120
210              0.187
312              0.27
416              0.48
520              0.75
625              0.422
728              1.471
832              1.921
940              3.00

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Also, read

What is BBS ( Bar Bending Schedule)?

How to Calculate Quantity of Material For Plastering

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