How To Calculate Steel Quantity From Drawing 

We only have drawings. So, we  calculate steel quantity  in drawings.

But the basic thing is simple.

The Basic Formula For Calculating Steel Quantity

You need to go through these three steps.

1.Getting The Number Of Steel Bars:

, the drawing of a structure has  10mm and 12mm diameter bar, you need to count both sizes of bars separate.

So count the same length bars together.

2. Get The Length Of Bars

Get the length of a bar in the drawing and multiply the length with the numbers of bars you counted in step

3. Get The Weight Of Bars

Simple!

Isn’t it?

How To Calculate The Steel Quantity From Drawings?

A building has different structural parts. 

How To Calculate Steel For Footing  in Drawings?

1. Get The Number Of Steel Bars:

• 16 mmØ bar

Number of bars = {(width of footing – 2 × clear cover) ÷ Spacing of bars} + 1
= {(4′ – 2 × 3″) ÷ 4″} + 1
= {3½’ ÷ 4″} + 1
= 11.60 nos
Say, 12 nos.

• 20 mmØ bar

Number of bars = {(length of footing – 2 × clear cover) ÷ Spacing of bars} + 1

= {(6′ – 2 × 3″) ÷ 4″} + 1
= {5½’ ÷ 4″} + 1
= 17.66 nos
Say, 18 nos.

2. Get The Length Of Bars

• 16mmØ bar

Length of a bar = Length of footing – 2 × clear cover + 2 × end hook
= 6′ – 2 × 3″ + 2 × 6″
= 6½’.

Total length of 16mmØ bar = number of bars × length of a bar
= 12 x 6½’
= 78 feet

• 20mmØ bar

Length of a bar = width of footing – 2 × clear cover + 2 × end hook
= 4′ – 2 × 3″ + 2 × 6″
= 4½’.

Total length of 20mmØ bar = number of bars × length of a bar
= 18 x 4½’
= 81 feet

3. Calculating The Weight Of Steel Bars

Weight of steel bars = Length of bars × unit weight

• Weight of 16mmØ bar

= 78′ × 0.48
= 37.44 kilogram
Say, 38 kilogram.

• Weight of 20mmØ bar

= 81′ × 0.75

= 60.75 kilogram
Say, 61 kilogram.

You may need 10mmØ bars to bind the footing net all around. Calculate these as you require.

How To Calculate The Steel Quantity From Drawing For Neck Column

In the above drawing, the column has three sizes of bars.
20mmØ and 25mmØ bar as main reinforcement and 10mmØ bar as stirrups.

1.Getting Number Of Bars

• 20mmØ

Number of bars = 6 (specified in drawing).

• 25mmØ

Number of bars = 4 (specified in drawing).

• 10mmØ

Number of stirrups = (Clean height of column ÷ spacing of stirrups) + 1

Getting the clear height of columns is a little bit tricky.

You need to study the footing drawing carefully.

Sometimes there is a note in the footing drawing that how depth the footing should be placed below the ground.

From there, you’ll get the clear height of neck columns.

For the clear height of floor columns, you need to depend on the architectural drawing.

There should be a cross sectional plan in architectural drawing book.

From there you’ll get the clear height of floor columns.

Let’s assume, the clear height of the column we are calculating steel for is 8 feet.

But, when you calculate steel quantity for neck/short column you need to add the thickness of footing with the clear height.

In that case the height of the column will be,

= Clear height of column + thickness of footing.

So, number of stirrups for neck column is,

= (Clear height of column + thickness of footing) ÷ spacing of stirrups

= {(8′ + 1′) ÷ 4″} + 1

= 28.27

Say, 29 nos.

We also need to use at least two numbers of stirrups in the beam-column joint. It’s sometimes recommended in the general notes of structural drawing.

So, total required number of stirrups are,

=29 + 2
= 32 nos.

2. Get The Length Of Bars

Length of a bar ( for neck column)= clear height of column + thickness of 1st-floor beam + lapping for future column + thickness of grade beam + depth of footing + thickness of footing + end hook.

• 20mmØ

length of a 20mmØ bar,

= 8′ + 1′ + 60D + 1′ + 3′ + 1′ + 1½’

[Lap length of columns is normally calculated as 60D. However, you’ll get notes about this in structural drawings. You should follow that.]

= 15½’ +60D
= 15½’ +60 × ¾” (20mm = ¾”)
=15½’ +  45”
= 19.25 feet.

As we have 6 numbers of bars, so the total length of 20mmØ bars is,

=6 × 19.25
= 115.5 feet

• 25 mmØ

Length of a 25mmØ bar is,

= 15½’ +60D (see how we calculated the length of a 20mmØ bar)
= 15½’ +60 × 1” (25mm=1”)
= 15½’ +60”
= 20½ feet.

Total length of 25 mmØ bars

= 4 × 20½ (We have 4 numbers of 25mmØ bar in our drawing).

= 82 feet.

• 10mmØ bar as strirrups

Length of a bar of a stirrup = 2 × (Legnth of column + width of column) – 4 × clear cover + 2 × hook
= 2 × (43” + 23”) – 4 × 3” + 2 × 3”
= 2 × 66” – 12” + 6”
= 132” – 12” + 6”
=126”
=10½’

The total length of bars for stirrups,
= 32 × 10½’ (Numbers of stirrups, we calculated above, are 32 nos)
= 336‘

3. Calculating The Weight Of Steel Bars

Weight of steel bars = Length of bars × unit weight

• 20 mmØ bar

= 115.5× 0.75
=73.12 kilogram.

• 25 mmØ bar

= 70 × 1.17
=81.90 kilogram.

• 10 mm bar

= 336‘ × 0.19
=63.84 kilogram.

How To Calculate The Steel Quantity For Beam From Drawing

1.Getting Number Of Bars

• 20 mmØ dia bar

Number of 20mmØ longitudinal bars in top and bottom,

=3 + 3
=6 nos.

Number of 20 mmØ extra top bar on support1 = 2 nos.

Number of 20 mmØ extra top bar on support2 = 2 nos.

Number of 20 mmØ extra bottom bars = 2 nos

• 10 mmØ bar

Number of stirrups for 1st span,

= (22′-8″)/4″ +1 = 69 + 1 = 70 nos.

Number of stirrups for 2nd span,

= (8′-4″)/4″ + 1 = 25 + 1 = 26 nos.

Total number of stirrups = 70 + 26
= 96 nos.

2. Get The Length Of Bars

• 20mmØ bar

Length of a longitudinal bar = Beam length – 2 × clear cover + 2 × end hook + lap length (if required)

= 36’ – 2 × 1½” + 2 × 12D (Lap length isn’t required here as we don’t need more than a full-length bar. D=20mm=¾”)
=  36’ – 3” + 18”
=37.25 feet

Total length of 20mmØ longitidinal bars,
= 6 × 37.25
=223.50 feet.

Length of a 20 mmØ extra top bar on support1,

= Extended length from support + width of support – clear cover + end hook (if the bar on end support)
= (7′-5″) + 20″ – 1½” + 9½”
= 9.75 feet

Total length of extra top bars on support1,
= 2 × 9.75
= 19.5 feet

Length of a 20 mmØ extra top bar on support2,

=(7′-5″) + (11′-8″) – 1½” + 9½”
=19.75 feet

Total length of extra top bars on support2,
= 2 × 19.75
= 39.5 feet

Length of a 20 mmØ extra bottom bar

=Distance between supports – 2 × distance between extra bottom bar and nearest support
=(22′-8″) – 2 × (2′-10″)
= 17 feet

The total length of the extra bottom bar,
= 2 × 17′ (there are 2 bars for Eb shown in the image above)
= 34 feet.

So, The total length of 20mm bars in the beam is,
=223.5 + 19.5 + 39.5 + 34
= 316.50 feet.

• 10mmØ bar as strirrups

Length of a bar of stirrup,
= 2 × (height of beam + width of beam) – 4 × clear cover + 2 × hook
= 2 × (24” + 12”) – 4 × 1½” + 2 × 3”
= 2 × 36” – 6” + 6”
= 72”
=6 feet.

The total length of bars for stirrups,= 96 × 6’ (Numbers of stirrups, we calculated above, are 96 nos)
= 576 feet.

3. Calculating The Weight Of Bars

Weight of steel bars = Length of bars × unit weight

• 20 mmØ bar

= 316.50 × 0.75
=237.37 kilogram.

• 10 mmØ bar

= 576 × 0.19
=109.44 kilogram.

How To Calculate The Steel Quantity Of Slab From Drawing

Different types of reinforcement are designed for different types of slab.

So calculating steel quantity of slab varies depending on the reinforcement design.

I’ll show you the process of calculating steel for a double reinforced slab.

1.Getting Number Of Bars

Numbers of bars =( length/width of slab ÷ spacing of reinforcement)+1

• 10mmØ bar

1- 10mmØ 5″ c/c bottom and top

Number of bars ={ (9′-9″) ÷ 5″}+1
= 24.21 nos.
Say, 25 nos.

As this reinforcement will be used in both the top and bottom, so the number of bars,
= 25 × 2
= 50 Nos.

2- 10mmØ 6″ c/c bottom and top

Number of bars ={ (15′-4″) ÷ 6″}+1
= 31.66 nos.
Say, 32 nos.

As this reinforcement will be used in both top and bottom, so the number of bars,
= 32 × 2
= 64 Nos.

2. Get The Length Of Bars

You can take the length or width of slab as a length of a bar.

• 10mmØ bar

1- 10mmØ bar 5″ c/c bottom and top

Length of a bar is,

= 9′-9″
=9.75 feet.

The total length of bars = number of bars × length of a bar
= 50 × 9.75
= 487.50 feet

2- 10mmØ bar 6″ c/c bottom and top

length of a bar is,
= 15′-4″
=15.33 feet.

The total length of bars = number of bars × length of a bar
= 64 × 15.33
= 981.12 feet

Total length of 10 mmØ bars is,
= 487.50+981.12
=1468.62 feet.

3. Calculating The Weight Of Bars

Weight of steel bars = Length of bars × unit weight

• 10 mmØ bar

= 1468.62 × 0.19
=279.04 kilogram.

Conclusion

You may have noticed that I sometimes didn’t consider the clear cover, bend deduction length, etc. in the above steel calculation.

That’s because we calculate steel quantity mainly for purchasing the steel. So, that minor length due to clear cover, etc. don’t have a big impact. So can ignore this.

But before purchasing steel bars, don’t forget to add 10% extra quantity for wastage.

Calculating steel quantity from drawing isn’t that hard task if you understand structural drawings.

The thing is simple.

You just need to get the total length of same size bars. Then convert that length into the weight.

Your Opinion
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