How to Calculate Weight of Steel Bars?

How to Calculate the Unit Weight of Steel Bars

There is a formula to calculate the unit weight of steel bars. I’ll come to that point later.

Why do we need to know the unit weight of steel bars?

When we estimate the steel bars of a Reinforced Concrete member we actually get the length of those bars.

For example, 1000 feet 20mmø bar or 500 feet 16mmø bar, etc (ø – a symbol of diameter).

But steel bar suppliers measure the steel bars as weight. So we have to order them in weight for purchasing. The weight of steel bars can be expressed in kilogram or quintal or ton. [1 quintal = 100 kg, 1 ton = 1000 kg]

Now come to the point.

How to Calculate The Weight of Steel Bars

We often use a formula for Calculating the weight of Steel Bars.

The formula converts the length of steel bars to weight. We can also use the formula to know the unit weight of steel bars of different sizes.

The Formula is, D²L/162

Where,
D = Diameter of steel bar in millimeter
L = Length of steel bars in meter

Understanding the Formula

We know, the weight of any material is,

=Cross-sectional area of the material × Length of the material × Density of the material

For steel bar, this is also the same.

The weight of steel bars (W)= Cross-sectional area of steel bar (A) × Length of steel bar (L) × Density of steel bar (ρ).

That means,

W = A x L x ρ

Where,
A = Area = πD²/4 
π (pai) = 3.14
D = Diameter of steel bar in milimeter (steel bar size is measured in millimeter).
L = Length of steel bar in meter
ρ (Rho) = Density of steel bar = 7850 kg/m³

Therefore,

W = 3.14 x D²/4  x L x 7850

But there are two conflicting units in the formula. Those are millimeter for D and meter for ρ (Rho).

We have to convert either D from millimeter to meter or ρ from meter to millimeter.

Let’s convert D from millimeter to meter.

1 millimeter = 1/1000 meter

Let’s implement this to the formula,

W= 3.14 x D²/(4x1000x1000) x L x 7850

= D²L/162

Using this formula we can calculate the weight of steel bars.

Calculating Weight of Steel Bars Per Meter

Keep in mind that the unit of D (diameter of the bar) should be in millimeter and L (Length of the bar) should be in meter in this formula.

Let’s see some examples.

Example-1:
How to calculate the weight of 100 meters long 16mmø bar?

In this example,

D= 16 millimeter
L = 100 meter

So,

W = D²L/162

= 16² x 100/162

= 158 kilogram (approx)

Answer: Weight of the 100 meters long 16mmø bar is 158 kilogram.

Example-2
How to calculate the weight of 100 meters long 20mmø bar?

In this example,

D = 20 millimeter
L = 100 meter

So,
W = D²L/162

= 20² x 100/162

= 247 kilogram (approx)

Answer: Weight of the 100 meters long 20mmø bar is 247 kilogram.

Unit Weight of Steel Bar When Length is in Meter

If you put 1-meter length for each diameter of steel bars in the formula then you’ll get the unit weight.

Let’s see.

W = D²L/162

Unit weight of,

• 10mmø bar = 10² x 1/162 = 0.617 kg/m
• 12mmø bar = 12² x 1/162 = 0.888 kg/m
• 16mmø bar = 16² x 1/162 = 1.580 kg/m
• 20mmø bar = 20² x 1/162 = 2.469 kg/m
• 25mmø bar = 25² x 1/162 = 3.858 kg/m

If you multiply the length of estimated bars with this unit weight you’ll get the total weight of steel bars for your reinforced concrete member.

For example, total weight of 1000 meter long 25mmø steel bar is,

1000 x 3.858 = 3858 kilogram.

So far we have seen the unit weight for each diameter of steel bar in meter basis. That means the weight of a bar per meter.

But what if you estimate the steel bar length in the foot. What will be the formula to calculate the steel bar’s weight if the length of the bar is on the foot?

You May Want to Read:

Concrete Cover for Reinforcement Bar
Types of Rebar Support in RCC Member

Calculating Weight of Steel Bars When Length is in Foot

Again,

Weight = A x L x ρ

= 3.14 x D²/(4 x 304.80 x 304.80) x 222

= D²L/533

Where,
D = Diameter of bar in mm (1 foot = 304.80 mm)
ρ (Rho) = 7850 kg/m³ = 222 kg/ft³ (actually it is 222.287 kg/ft³)

Keep in mind that you always should use D as millimeter and L as feet in this formula.

Unit Weight of Steel Bar When The Length is in Foot

If you calculate a 1-foot length of any diameter of steel bar you will get the following result and that will be the unit weight of steel bars per foot length.

Unit weight of,

• 10mm ø bar = 10² x 1/533 = 0.188 kg/ft
• 12mm ø bar = 12² x 1/533 = 0.270 kg/ft
• 16mm ø bar = 16² x 1/533 = 0.480 kg/ft
• 20mm ø bar = 20² x 1/533 = 0.750 kg/ft
• 25mm ø bar = 25² x 1/533 = 1.172 kg/ft

If you multiply the estimated length of steel bars with these unit weights you’ll get the total weight of steel bars.

For example,
Weight of 1000 feet long 10mm ø bar is,

1000 x 0.188 = 188 kg.