Steel bars are commonly used in construction of reinforced concrete elements (such as columns ,beams, footings and slabs) since concrete is not capable of resisting the tension forces. In this article, we go through the Weight Calculation of Steel Bars, which is very beneficial in quantity surveying as the total cost is determined according to the weights obtained.
Definition of Unit Weight
The unit weight, also known as the specific weight, is:
the weight per unit volume of a material.
The units can be anything such as kg/m3, pound/ft3, etc. The important thing is that it is weight unit divided by volume unit.
Unit Weight of Steel
The unit weight of steel (we also call it density) is approximately:
- 78.5 kN/m3
- 7850 kg/m3
- 7.85 g/cm3
- 490 lbs/ft3
- 13231 lbs/yd3
What Diameters of Steel Bars Used In Construction?
The different steel bar diameters that are used in construction are:
- 8 mm
- 10 mm
- 12 mm
- 16 mm
- 20 mm
- 22 mm
- 25 mm
- 32 mm
- 40 mm
Small bar sizes up to 25 mm are used in normal applications such as residential, commercial and institutional purposes.
Diameters above 25 mm are used in special applications such as bridges and dams.
Length of Steel Bars
Usually, steel bars are provided in 12 m length.
Formula for Weight Calculation of Steel Bars
The general formula is:
Weight = Unit Weight (density) x Volume
Formula for Weight Calculation of Flat Steel Bars
A flat steel bar is specified by its width and thickness.
Formula is:
Weight of Steel Bar = Volume of Steel Bar x Unit Weight of Steel
Weight of steel Flat bar = (width * length * thickness) x 7850 (kg/m3)
Ex: Calculate the weight of MS Flat bar of length = 1 m, width = 40 mm and Thickness = 20 mm
Weight of steel bar = (1 * .04 * .02) * 7850 = 6.28 kg. This is to say that the weight of 1 m of steel is 6.28 kg. So, if have a total length of bars equal to 125 m, we can calculate the total weight as:
Total length * weight of 1 m
Formula for Weight Calculation of Steel Bars (Rods)
Let us go together through the derivation of the formula for unit weight of steel bars (weight per meter):
Assume a steel bar with a diameter of D and a length is L.
Weight of Steel Bar (W) = Unit Weight of Steel (7850) x Volume of Bar
Volume of Bar = πD²/4
Weight of Steel Bar (W) = 7850 * πD²/4
At this point, we have D in meters and the 7850 in kg/m3. If we want to use the diameter in mm, we need to convert it to m:
D² (mm) / 1000²
W = 7850 * π/4 x D²/1000²
W = D²/162 kg/m, where D is in mm —-> Eq. 1
if the total length of bar is L, total weight will be W * L:
W = L*D²/162 kg, where D is in mm —-> Eq. 2
If you want to calculate the weights per feet, the 162 is changed to 533
Weight of Steel Bars
Using the previous equations, we can calculate the weight of various steel bars:
Assuming the length of the bar is 1 m, we use equation 1:
Weight of 6 mm Steel Bars
For bar size of 6 mm ø bar:
W = (6)2 / 162 = 0.222 kg/m
Weight of 6 mm steel bar is 6.32 kg per meter
Weight of 8 mm Steel Bars
For bar size of 8 mm ø bar:
W = (8)2 / 162 = 0.395 kg/m
Weight of 8 mm steel bar is 0.395 kg per meter
Weight of 10 mm Steel Bars
For bar size of 10 mm ø bar:
W = (10)2 / 162 = 0.617 kg/m
Weight of 10 mm steel bar is 0.617 kg per meter
Weight of 12 mm Steel Bars
For bar size of 12 mm ø bar:
W = (12)2 / 162 = 0.889 kg/m
Weight of 12 mm steel bar is 0.889 kg per meter
Weight of 16 mm Steel Bars
For bar size of 16 mm ø bar:
W = (16)2 / 162 = 1.58 kg/m
Weight of 16 mm steel bar is 1.58 kg per meter
Weight of 20 mm Steel Bars
For bar size of 20 mm ø bar:
W = (20)2 / 162 = 2.47 kg/m
Weight of 20 mm steel bar is 2.47 kg per meter
Weight of 25 mm Steel Bars
For bar size of 25 mm ø bar:
W = (25)2 / 162 = 3.86 kg/m
Weight of 25 mm steel bar is 3.86 kg per meter
Weight of 32 mm Steel Bars
For bar size of 32 mm ø bar:
W = (32)2 / 162 = 6.23 kg/m
Weight of 32 mm steel bar is 6.23 kg per meter
Summary:
Unit Weight of Steel kilogram per feet
For bar size of 6 mm ø bar:
W = (6)2 / 533= 0.067 kg/ft
If the bar size is 8 mm ø bar:
W = (8)2 / 533 = 0.12 kg/ft
If the bar size is 10 mm ø bar:
W = (10)2 / 533 = 0.188 kg/ft
If the bar size is 12 mm ø bar:
W = (12)2 / 533 = 0.27 kg/ft
If the bar size is 16 mm ø bar:
W = (16)2 / 533 = 0.48 kg/ft
If the bar size is 20 mm ø bar:
W = (20)2 / 533 =0.75 kg/ft
If the bar size is 25 mm ø bar:
W = (25)2 / 533 = 1.174 kg/ft
If the bar size is 32 mm ø bar:
W = (32)2 / 533 = 1.925 kg/ft
Unit Weight of Steel Ib per feet
Unit weight of:
- 8 mm or #2.5 rebar/steel is 0.265 lb/ft
- 10 mm or #3 rebar/ steel is 0.376 lb/ft
- 12 mm or #4 rebar/ steel is 0.668 lb/ft
- 16 mm or #5 rebar/ steel is 1.043 lb/ft
- 20 mm or #6 rebar/ steel is1.502 lb/ft
- 25 mm or #8 rebar/ steel is 2.67 lb/ft
- 32 mm or #10 rebar/ steel is 4.303 lb/ft
- 36 mm or #11 rebar/ steel is 5.313 lb/ft
Weight Calculation of Steel Bars on Construction Site
The measures that must be taken in order to determine how much steel is present on the building site or how much steel is placed into the truck at the time of delivery are as follows.
STEP ONE: Know what are the different diameters in the package
Assume we have 10, 12 and 16 mm.
STEP TWO: Count the number of bars for each diameter
10 mm = 120 nos.
12 mm = 50 nos.
16 mm = 60 nos.
STEP THREE: Get the unit weight of bars
Calculate the unit weight of steel per meter as we did earlier in the article:
10 mm = 0.62 kg/m
12 mm = 0.89 kg/m
16 mm = 1.58 kg/m
STEP FOUR: Get the total weight of each bar diameter
Total Weight of a certain diameter = Number of bars * Unit weight * Length of one Steel bar (12 m)
For 10 mm bars, the total weight = 120 * 0.62 * 12 = 892.8 kg
For 12 mm bars, the total weight = 50 * 0.89 * 12 = 534 kg
For 16 mm bars, the total weight = 60 * 1.58 * 12 = 1137.6 kg
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