Footing Rebar Calculator

Last updated: 27 Nov 2025 | Author: Brij | Review By: Irshad

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A simple footing rebar calculator with minimal inputs. Calculate the number of rebars, total rebar length, and rebar weight using easy formulas. Includes step-by-step calculation, formulas, and a complete example.

Footing Length:

Footing Width:

Rebar Diameter:

Rebar Spacing:

Footing Rebar Calculation Results

Number of Longitudinal Rebars:

count

Number of Transverse Rebars:

count

Total Rebar Length:

Total Rebar Weight:

Designing a footing requires proper reinforcement so the concrete can safely carry the load. A Footing Rebar Calculator makes this job easy by calculating how many rebars you need, plus their total length and weight.

Formulas Used in Footing Rebar Calculator

1. Number of Longitudinal Rebars

These bars run along the length of the footing.

Formula

$N_{long} = \frac{Footing\ Width}{Rebar\ Spacing} + 1$

2. Number of Transverse Rebars

These bars run along the width of the footing.

Formula

$N_{trans} = \frac{Footing\ Length}{Rebar\ Spacing} + 1$

3. Total Rebar Length

Total length of steel used for both directions.

Formula

$Total\ Length = (N_{long} \times Footing\ Length) + (N_{trans} \times Footing\ Width)$

4. Total Rebar Weight

Weight of steel depends on rebar diameter.

Formula

$Weight = Total\ Length \times Unit\ Weight\ (kg/m)$

Note: Unit weight for rebar is:

$Unit\ Weight = \frac{d^2}{162}$

(where d = diameter in mm)

Example Calculation

Let’s take a simple footing size:

Footing Length = 8 ft (2.44 m)
Footing Width = 4 ft (1.22 m)
Rebar Spacing = 6 in (0.152 m)
Rebar Diameter = 12 mm

1. Number of Longitudinal Rebars

$N_{long} = \frac{1.22}{0.152} + 1 = 9.03 \approx 10$

2. Number of Transverse Rebars

$N_{trans} = \frac{2.44}{0.152} + 1 = 17.05 \approx 18$

3. Total Rebar Length

$Total\ Length = (10 \times 2.44) + (18 \times 1.22)$

$Total\ Length = 24.4 + 21.96 = 46.36\ m$

4. Total Rebar Weight

First compute unit weight:

$Unit\ Weight = \frac{12^2}{162} = 0.888\ kg/m$

Now total weight:

$Weight = 46.36 \times 0.888 = 41.2\ kg$

FAQs

1. What is rebar used for in a footing?

Rebar strengthens the concrete footing by resisting tension forces. Concrete is strong in compression but weak in tension, so rebar prevents cracks and increases load-carrying capacity.

2. How do I know how many rebars my footing needs?

The number of rebars depends on the footing’s length, width, and spacing. A simple rule is to divide the footing dimension by the rebar spacing and add one. A footing rebar calculator makes this easy.

3. What rebar size is normally used for footings?

Most residential footings use #4 (12 mm) or #5 (16 mm) rebars. The exact size depends on soil conditions, load, and building code requirements.

4. Do I need two layers of rebar in a footing?

Small residential footings usually have one layer at the bottom. Larger or heavily loaded footings may require two layers or additional reinforcement as per structural design.

5. How much rebar overlap (lap length) is needed in a footing?

Typical lap length is 40 times the bar diameter (40d). For example, a 12 mm bar needs about 480 mm lap. This ensures proper load transfer between rebars.

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