Slab rebar quantity calculator
This calculator estimates the reinforcing steel in a solid concrete slab from its concrete volume: area × thickness gives the volume in m³, then volume × steel ratio (by default 95 kg per m³) gives the steel weight in kg. It is an early estimate for pricing and BOQs; the final quantity comes from the bar bending schedule on the structural drawings.
Calculator
- Reinforcing steel
- 4,256 kg (4.26 t)
- Slab concrete
- 44.8 m³
Method, step by step
- Multiply the slab area in m² by the slab thickness in metres to get the concrete volume in m³.
- Multiply the volume by the steel ratio in kg per m³ to get the steel weight in kg.
- Divide by 1000 to convert to tonnes, the usual unit for steel in BOQs and quotations.
Worked example
Inputs
- Slab area (m²): 320
- Slab thickness (m): 0.14
- Concrete volume = area × thickness = 320 × 0.14 = 44.8 m³.
- Steel weight = volume × steel ratio = 44.8 × 95 = 4,256 kg.
- In tonnes: 4,256 ÷ 1000 = about 4.26 t.
Result
- Reinforcing steel
- 4,256 kg (4.26 t)
- Slab concrete
- 44.8 m³
Assumptions and default ratios
| Ratio | Default value |
|---|---|
| Slab steel ratio | 95 kg/m³ |
- The steel ratio is an editable default. In practice it depends on spans, loads and slab type, so use the structural design value when you have it.
- The method assumes a solid slab of constant thickness. Beams, laps and waste are not included.
Frequently asked questions
How many kg of steel are there in one m³ of slab concrete?
The calculator uses 95 kg per m³ as a default. It is an estimate, not a constant: long spans and heavy loads need more, short spans less. Change it under the ratios if you have a figure from a similar project or from the designer.
Does it work for hollow-block (hourdi) or flat slabs?
It is built on a steel-to-concrete ratio for a solid slab. For a hollow-block slab, enter the actual concrete volume without the blocks and a suitable ratio; for a flat slab, enter the real thickness and the design ratio.
Does the result include waste and laps?
No. It is a net weight from the ratio; add the waste and lap allowance you use before ordering.
How do I convert kg to tonnes?
Divide the weight in kg by 1000. The calculator shows both.
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.