Footing rebar quantity calculator
This calculator works out the bottom mesh of isolated footings: the bars in each direction are the net size after cover divided by the spacing, plus one; total length × weight per metre (D² ÷ 162) gives the steel. It also gives the footing concrete, cement bags, sand and gravel from the default ratios.
Calculator
- Bottom mesh steel
- 1,141 kg (1.14 t)
- Bars per footing
- 13 along the length + 16 along the width
- Total bar length
- 721.8 m
- Footing concrete
- 36 m³
- Cement
- 252 bags
- Sand / gravel
- 16.2 / 30.6 m³
Method, step by step
- Subtract the concrete cover on both sides from the footing length and width to get the net length and width.
- Bars parallel to the length = whole part of (net width ÷ spacing) + 1; the same for bars parallel to the width.
- Bar length per footing = bars in each direction × their net length; multiply by the number of identical footings.
- Weight per metre = D² ÷ 162; total weight = total length × weight per metre.
- Concrete = length × width × depth × count; cement = volume × 350 kg ÷ 50 kg per bag, rounded up.
Worked example
Inputs
- Length (m): 2.5
- Width (m): 2
- Footing depth (m): 0.6
- Number of footings: 12
- Bar diameter (mm): 16
- Bar spacing (cm): 15
- Concrete cover (cm): 7.5
- Net length = 2.5 - 2 × 0.075 = 2.35 m, net width = 2 - 2 × 0.075 = 1.85 m.
- Bars along the length = whole part of (1.85 ÷ 0.15) + 1 = 13; bars along the width = whole part of (2.35 ÷ 0.15) + 1 = 16.
- Bar length per footing = 13 × 2.35 + 16 × 1.85 = 60.15 m; for 12 footings = 721.8 m.
- Weight per metre of a 16 mm bar = 16² ÷ 162 = 1.58 kg/m.
- Steel weight = 721.8 × 1.58 = 1,141 kg (1.14 t).
- Footing concrete = 2.5 × 2 × 0.6 × 12 = 36 m³; cement = 36 × 350 ÷ 50 = 252 bags, rounded up.
Result
- Bottom mesh steel
- 1,141 kg (1.14 t)
- Bars per footing
- 13 along the length + 16 along the width
- Total bar length
- 721.8 m
- Footing concrete
- 36 m³
- Cement
- 252 bags
- Sand / gravel
- 16.2 / 30.6 m³
Assumptions and default ratios
| Ratio | Default value |
|---|---|
| Weight-per-metre divisor (D² ÷ divisor) | 162 number |
| Cement in concrete | 350 kg/m³ |
| Cement bag weight | 50 kg/bag |
| Sand ratio | 0.45 m³ per m³ of concrete |
| Gravel ratio | 0.85 m³ per m³ of concrete |
- One bottom mesh with the same diameter and spacing both ways, straight lengths only: no hooks, laps, top mesh or column starter bars.
- The diameter, spacing and cover in the example are illustrations; use the values on your reinforcement drawing.
- The cement, sand and gravel ratios are editable defaults and follow the concrete mix approved for your project.
Frequently asked questions
How do I count the bars in a footing?
Divide the net dimension across the bars (after the cover on both sides) by the spacing, keep the whole part and add one. A net width of 1.85 m at 15 cm gives 12 + 1 = 13 bars.
Why is the weight per metre D² ÷ 162?
The bar section is π × D² ÷ 4; multiplied by the density of steel (about 7850 kg/m³) it comes to roughly D² ÷ 162 kg per metre with D in millimetres.
Are hooks and the top mesh included?
No. The result is the bottom mesh in straight lengths. Add hooks or a top mesh from your drawing, or price them as a separate line with the rebar weight calculator.
Add the result to your project BOQ in Ta3mir
In Ta3mir the same calculators work inside your project: send a result to a BOQ line in one click and save your own default ratios for every calculation.