An ordinary person can estimate reinforcement as a lump sum. I see many people estimate reinforcement as a percentage of concrete volume. Such as **2%** or **1.5%** of concrete volume.

But as a construction professional you shouldn’t estimate rebar quantity as a percent of concrete volume. You should estimate that as shown in the structural drawing.

Estimating rebar quantity is easy. All you have to get the cutting length for each type of bar in the beam.

In this post, I’ll discuss **how to estimate beam reinforcement** from the drawing.

We’ll use the following image as a structural drawing of the beam.

## How to Estimate Beam Reinforcement?

For estimating beam reinforcement, You first need to know which types of bars are available in the beam.

From the image above we have found –

- Top longitudinal bar,
**T – 3D20** - Bottom longitudinal bar,
**B – 3D20** - The extra top bar on support1,
**Et1 – 2D20** - The extra top bar on support2,
**Et2 – 2D20** - Extra bottom Bar,
**Eb – 2D20** - Stirrup,
**S1 – D10 @ 4″ c/c**

If you don’t know the name of bars on different locations in a beam then read the following post.

14 Terms About Beam Reinforcement a Supervisor Should Be Familiar With

You will also need the following data to estimate the beam reinforcement –

- Clear cover for reinforcement
- Lap length
- Bend length

You’ll get this data from the general notes sheet of structural drawing.

**Read More:**

Concrete Cover for Reinforcement Bar

17 Technical Terms about Reinforcement a Construction Supervisor Should Know

4 Terms to Understand to Truly Estimate Rebar Quantity

That’s fine.

We have enough data to estimate the beam reinforcement. Let’s estimate.

### Top Longitudinal Bar (T)

Apply the following formula to get the *cutting length* of the *top longitudinal bar*.

**Cutting Length of top longitudinal bar is,**

*= Length of beam – 2 × clear cover + 2 × bend length – 2 × bend deduction length + lap length*

*Length of beam:* 20″ + (22′-8″) + 20″ + (8′-4″) + 20″ = **36′** (from above image)

*Clear cover:* **1½”**

*Bend length:* 12D = 12 × 20 = 240 mm, say **9½”**

*Bend deduction length:* Bend deduction length for 90° bend is equal to two times of bar dia = 2 × 20 mm = 40mm = **1½”**

So, the *cutting length *of the top longitudinal bar is,

= 36′ – 2 × 1½” + 2 × 9½ – 2 × 1½” + 0

= **37′-1″**.

There are **Three numbers** of the top longitudinal bar in the above image. So the total length of the top longitudinal bar is,

= 3 × (37′-1″)

= **111′-3″**.

We know the full length of a reinforcing bar is about **40′**. The length of a top longitudinal bar, we are estimating, doesn’t exceed the length of a full bar. So you don’t have to add lap length.

### Bottom Longitudinal Bar (B)

The formula for calculating the cutting length of the **bottom longitudinal bar** is the same as the formula for the **top longitudinal bar**. So the length is also the same as **T1**. That is **37′-1″**.

So the total length of the **B1** bar is,

= number of B1 bar × cutting length of a B1 bar

= 3 × (37′-1″)

=**111′-3″**.

### Extra Top Bar on Support1 (Et1)

Calculating cutting length of extra top bar follow the following formula –

*Cutting length of Et1* = extended length from support + width of support – clear cover + bend length – bend deduction length

*Extended length from support*: **7′-5″**

*Width of support*: **20″**

*Clear cover*: **1½”**

*Bend length*: **9½”**

*Bend deduction length*: **1½”**

So the cutting length of **Et1** is,

= (7′-5″) + 20″ – 1½” + 9½” – 1½”

= **9′-7½”**

There are two numbers of **Et1** bar shown in the drawing (image above). So the total length of **Et1** is,

=2 × (9′-7½”)

= **19′-3″**

### Extra Top Bar on Support2 (Et2)

*Extended length from support*: **7′-5″**

*Width of support*: width of support for Et2 should be the width of *support2 + distance between support2 and support3 + width of support3* = 20″ + (8′-4″) + 20″ = **11′-8″**

*Clear cover*: **1½”**

*Bend length*: **9½”**

*Bend deduction length*: **1½”**

So, cutting length of Et2 = (7′-5″) + (11′-8″) – 1½” + 9½” – 1½”

= **19′-7½”**

Total length of Et2 = 2 × (19′-7½”)

= **39′-3″**

### Extra Bottom Bar (Eb)

Cutting length of the extra bottom bar is,

=**Distance between support – 2 × distance between extra bottom bar and nearest support**

= (22′-8″) – 2 × (2′-10″)

=

**17′**

The total length of the extra bottom bar is,

= 2 × 17′ (there are 2 bars for Eb shown in the image above)

= **34′**

### Stirrup (S1)

For estimating stirrup you have to calculate the required number of stirrups for the beam and cutting length of the bar for a stirrup.

*Number of stirrup:*

Required number of stirrup for 1st span,

= (22′-8″)/4″ +1 = 69 + 1 = **70 nos**.

Required number of stirrup for 2nd span,

= (8′-4″)/4″ + 1 = 25 + 1 = **26 nos**.

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

Formula for calculating **cutting length of a stirrup’s bar is**,

= 2 × (a+b) + 24D (for 135° hook)

Where,

*a = length of stirrup’s long side*

*b = length of stirrup’s short side*

*D = dia of stirrup bar*

So cutting length of the bar is,

= 2 × (21″+9″) + 24 × 10

= 69½” (240 mm = 9½”)

= **5′-9½”**

Total length of bars for all stirrups,

= 96 × (5′-9½”)

= **556′**

__Summary:__

Total reinforcing bar we have estimated for the beam so far –

*20 mm ø bar –*

T = 111′-3″

B = 111′-3″

Et1 = 19′-3″

Et2 = 19′-7½”

Eb = 34′

So total 20 mm ø bar is,

= 111′-3″ + 111′-3″ + 19′-3″ + 19′-7½” + 34′ = **296′**.

*10 mm ø bar,*

S1 = **556′**.

But steel reinforcing bars are measured in kilograms in the market. So you have to convert the bar length to kilograms.

Unit weight of *10 mm ø bar* is **0.188 kg/ft** and *20 mm ø bar* is **0.75 kg/ft**.

* Related:* How to Calculate the Unit Weight of Steel Bars?

So reinforcement required for our example beam,

- 20 mm ø bar = 296′ × 0.75 =
**222 kilograms**. - 10 mm ø bar = 556 × 0.188 =
**105 kilograms**.

That’s it.

When you want to purchase reinforcing bar for the beam you should add **5%** more with your estimated quantity as wastage.

*You Turn:*

*How do you estimate beam reinforcement? Is there any quick technique? Please share in the comments below…*

sautya says

18/05/2019 at 8:57 amThank you so much

Liton Biswas says

19/05/2019 at 9:20 amYou’re welcome, sautya.