This is one of the most interesting and important topics for all the engineers working as site engineers or a designer. It is an important tool for preparing a detailed cost estimate in regard to the steel reinforcement and steel section in any structure. In this article, we will see how to calculate the unit weight of steel bars and other steel used in construction industries.
What is Unit Weight?
The unit weight of anything is the measure of the weight per unit volume of an object. It is also known as specific weight. It is typically expressed in units such as newtons per cubic meter (N/m3) or pounds per cubic foot (lb/ft2 ).
Formula for Unit Weight
The formula to calculate unit weight is:
Unit Weight (γ) = Weight (W) / Volume (V)
Where:
- Weight (W) is the total weight of the object.
- Volume (V) is the total volume of the object.
Unit Weight of Steel
The unit weight of steel is the weight of the meter length of the steel rod/bar used in the construction.
Important of unit weight
The unit weight of steel reinforcement is important for the engineers for designing the structure, preparing cost estimates and making the payment to the contractors and builders for the work carried out with the steel.
- This is to know the exact quantity of steel to be used in the construction.
- To procure the right quantity of steel bar.
- To make bill payments to the builder or contractor for the steel quantity used.
Method of Calculation Steel Bar
The density of the steel is 7850 kg/m3 or 7.85 g/cm3. The steel bar comes in various sizes ranging from 6mm to 40mm diameter. The calculation of the unit weight of the steel bar is done by knowing the diameter of the given bar.
The calculation of the unit weight of the bar is given by the formula: –
Where D is the diameter of steel and 162 is the constant
Derivation of Formula
As we know the density (γ) of the steel is 7850 kg/m3
Weight (W) of steel bar per meter = Volume X Density
\( Volume = Area X Length \)
\( W= Area X Length X Density \)
=π/4 X d2 X γ
= 0.785 X d2 X 1000 X 7850 kg / (1000 X 1000 X 1000) m3 [1 m = 1000 mm]
=785 X d2 X 0.00000785
=d2 /1 X 0. 00616225/1
=d2 /162.27
\( W=\frac{D^2}{162} \)
Therefore, the unit weight for the steel bar is \(\frac{D^2}{162}\)
Also, read: Types of Steels and Their Usage in Construction
Sample Calculation of Unit Weight of Steel Bar
For example, the unit weight of the 32 mm Ø bar is calculated
=(32 X 32)/162
=6.32 kg/m2
The unit weights for different diameters of bars are given in the Table below: –
| Sl.No. | Diameter of bar | Unit weight (kg/m2) |
|---|---|---|
| 1. | 8 | 0.39 |
| 2. | 10 | 0.62 |
| 3. | 12 | 0.89 |
| 4. | 16 | 1.58 |
| 5. | 20 | 2.47 |
| 6. | 25 | 3.85 |
| 7. | 32 | 6.32 |
Weight of Mild Steel plates and Flats
To calculate the unit weight of mild steel, it is essential to know the width of the plate or flat. The thickness of the plate and flat is considered in mm for the unit length of the sample formula for per meter length of the plates and flats calculates the weight of the steel plates and flats: –
Whereas x is: the unit weight of the steel plates and flats.
Steel Bar Unit Weight Calculator
| Thickness-mm | 5 | 6 | 8 | 10 | 12 | 14 | 16 | 18 | 20 | 22 | 25 | 28 | 32 | 36 | 40 |
| Weight-kg/sq.m | 39.25 | 47.10 | 62.80 | 78.50 | 94.20 | 109.90 | 125.60 | 141.30 | 157.00 | 172.80 | 196.25 | 219.80 | 251.20 | 282.00 | 314.00 |
Note: –
- Steel thickness above 4mm is known as plates.
Steel Plate Unit Weight Calculator
Also, read: Which is better: TMT and TMX steel?
FAQs:
Q: What is the unit weight of steel?
Answer: The unit weight of the steel is the weight per meter length of the given steel bar. It is calculated by using the formula \( \frac{D^2}{162} \) kg/m.
Therefore, the unit weight of different diameter steel bars is: –
8 mm = 0.39 kg/m
10 mm = 0.62 kg/m
12 mm = 0.88 kg/m
16 mm = 1.58 kg/m
20 mm = 2.46 kg/m
25 mm = 385 kg/m
32 mm = 6.32 kg/m
Q: How is the unit weight of the steel plate calculated?
Answer: To calculate the unit weight of the steel plate, the dimension of the plate is considered first. The volume of the steel plate is calculated and multiplied by the density of the steel.
Unit weight = Volume of steel x density of steel
The density of steel is 7850kg/m3
