Summary of Steel Weights
Table of Contents
What is steel?
Steel is a ductile material which is a common sight on the construction site and it is important for engineers to determine the unit weight of steel in designs. Steel is formed from iron with with a certain percentage of carbon, with small amounts of other metallic elements. These additional materials alter the properties of the steel. Steel is a magnetic material, and so is nickel, cobalt, and iron.
Steel weight and unit weight of steel bars
Unit weight of steel – The unit weight of steel or density of steel is defined as the ratio of mass of steel to volume of steel. Unit weight of steel is taken as 7850 kg/m3 or 78.5 kN/m3 and also taken as 8050 kg/m3 or 80.5 kN/m3.
Density of steel – 7850 kg/m3 to 8050 kg/m3 depending on the grade and type of manufacture.
However, it is standard practice to use the unit weight of steel in the design standard EN 1991-1-1 Table A.4 as 78.5 kN/m3 with a density of 7850 kg/m3. This is also used as the density of steel in other countries by civil engineers.
The weight of steel bars = density x volume
In the construction industry, the most common bar diameter type are 6mm, 8mm, 10mm, 12mm, 16mm, 20mm, 25mm, 32mm, 40mm.
Table : Weight of steel bars kg/m
| Bar size diameter (mm) | Perimeter (mm) | Weight of Bar (kg/m) |
| 6 | 18.85 | 0.222 |
| 8 | 25.1 | 0.395 |
| 10 | 31.4 | 0.619 |
| 12 | 37.7 | 0.888 |
| 16 | 50.2 | 1.579 |
| 20 | 62.8 | 2.469 |
| 25 | 78.5 | 1.388 |
| 32 | 100.5 | 6.313 |
| 40 | 125.6 | 9.864 |
Table : Weight of steel bars kg/ft
| Bar size diameter (mm) | Perimeter (mm) | Weight of Bar (kg/ft) |
| 6 | 18.85 | 0.728 |
| 8 | 25.1 | 1.296 |
| 10 | 31.4 | 2.031 |
| 12 | 37.7 | 2.913 |
| 16 | 50.2 | 5.180 |
| 20 | 62.8 | 8.100 |
| 25 | 78.5 | 4.554 |
| 32 | 100.5 | 20.712 |
| 40 | 125.6 | 32.362 |
Formula for calculation unit weight of steel
The density of steel = 7850 kg/m3
Weight of steel per meter = volume x Density [Volume = area x length]
= π/4 x d2 × 1000 × 7850 kg/m3 (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
Example 1: Calculation of 8mm steel weight of bars
Determine the weight of 5No. of 1m steel bars
The diameter of the steel bar = 8mm and the length of the bar is 1m
Area of circular bar = π/4 x d2
= π/4 x 82 = 50.27 mm2
Volume = Area x Length
= 50.27 x 1000 = 50270 mm3
Steel unit weight is 7850 kg/m3
Steel unit weight of 8mm bar = 50270/(109) x 7850 = 0.395 kg/m
The weight of the steel bars = 0.395 x 1 x 5 = 1.975 kg
Note – To convert mm3 to m3, multiply it by 1 x 109 (1,000,000,000)
Example 2: Calculation of 16mm steel weight of bars
Determine the weight of 10No. of 3m steel bars
The diameter of the steel bar = 16mm and the length of the bar is 1m
Area of circular bar = π/4 x d2
= π/4 x 162 = 201.06 mm2
Volume = Area x Length
= 201.06 x 1000 = 201061 mm3
Steel unit weight is 7850 kg/m3
Steel unit weight of 8mm bar = 201061/(109) x 7850 = 1.578 kg/m
The weight of the steel bars = 1.578 x 3 x 10 = 47.34 kg
Note – To convert mm3 to m3, multiply it by 1 x 109 (1,000,000,000)
Uses of steel bars
Steel bars are a common feature in reinforced concrete, which has been placed to take the tensile stresses in concrete. Concrete is good in compression and not in tension, hence we used steel bars to take these loads.
Reinforced concrete is used in the construction of columns, slabs, beams, dams and any other structure that needs concrete.
The density of concrete without steel reinforcement = 2400 kg/m3
When we consider the steel unit weight in concrete, we increase the density of concrete to 2500 kg/m3 to take into account the steel unit weight.
Yield Stress of Steel bars
The yield stress of high strength steel bars is 500 N/mm2 and is designated as Grade 500 in BS 4449. This is the commonly used stress in the United Kingdom.
Reinforcing steel are steel bars that are ‘ribbed’ and steel rods and wires refer to un-ribbed sections.
The United Kingdom used to employ ‘plain’ steel bar (un-ribbed) which were 250MPa (N/mm2). These steel bars are not used anymore, but older structures may still contain them, so analysis of older concrete structures needs to consider the lower yield strength.
Different countries need to refer to their manufacturers and national engineering codes to determine the yield strength of steel bars.
Yield strength of steel bars in concrete range from 600 -400 MPa (N/mm2).