// // Leave a Comment

How to Calculate the Unit Weight of Steel Bars

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

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

When we estimate the steel bars for a Reinforced Concrete member we get the length of that as a result. For example, 1000 feet 20mm ø bar or 500 feet 16mm ø bar, etc (ø - 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 kg or quintal or ton.

1 quintal = 100 kg
1 ton = 1000 kg or 10 quintal

Now come to the point.

How to calculate the weight of steel bars

How to Calculate the Weight of Steel Bars

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

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

The Formula: 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 a material is,

= Cross sectional area of the material x Length of the material x Density of the material

For steel bar this is also same.

Weight of steel bars= Cross sectional area of steel bar x Length of steel bar x Density of steel bar.

That means,

W = A x L x ρ

Where,
A = Area = πD²/4 
π (pai) = 3.14
D = Diameter of steel bar 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 unit in the formula. Those are millimeter for D and m for ρ (Rho).

We have to convert either D or ρ to same unit.

Let's convert D from millimeter to meter.

1 millimeter = 1/1000 meter

Lets 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.

You May Want to Read:
Types of Estimates in Building Construction
How to calculate materials for different-ratio concrete

Calculating Weight of Steel Bars When Length is in meter

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

Lets see some example.

Example-1:
How to calculate the weight of 100 meter long 16mm ø bar?

In this example,

D= 16mm
L = 100 m

So,

W = D²L/162

= 16² x 100/162

= 158 kg (approx)


Answer: Weight of the 100 meter long 16mm ø bar is 158 kg.

Example-2
How to calculate the weight of 100 m long 20mm ø bar?

In this example,

D = 20mm
L = 100 m

So,
W = D²L/162

= 20² x 100/162

= 247 kg (approx)

Answer: Weight of the 100 meter long 20mm ø bar is 247 kg.

Unit weight of steel bar per meter

Unit Weight of Steel Bar When Length is in Meter

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

Let's see.

W = D²L/162

Unit weight of,
  • 10mm ø bar = 10² x 1/162 = 0.617 kg/m
  • 12mm ø bar = 12² x 1/162 = 0.888 kg/m
  • 16mm ø bar = 16² x 1/162 = 1.580 kg/m
  • 20mm ø bar = 20² x 1/162 = 2.469 kg/m
  • 25mm ø 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 25mm ø steel bar is,

1000 x 3.858 = 3858 kg.

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

But what if you estimate the steel bar length in foot. What will be the formula to calculate the steel bar's weight if the length of bar is in 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 per feet

Unit Weight of Steel Bar When Length is in Foot

If you calculate 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.

Your Turn:
If you have any query about this post then ask me in the comments below. I'll reply as early as possible.

0 comments:

Post a Comment