Rebar Calculator
Reinforcing steel mass and cost for a concrete element.
Estimate the mass of reinforcing steel and its cost from the concrete volume and a reinforcement rate (kg of steel per m³ of concrete), using SA rebar benchmark rates.
- Reinforcing steel1 000 kg100 kg/m³ × 10 m³
- In tonnes1.00 t
- Estimated supply & fix costR 30/kgR 30 000
Steel content (kg per m³) is a rule-of-thumb by element type — confirm against the engineer's bending schedule. Supply-and-fix rate from NNAQS benchmark data.
A worked example
With the calculator’s starting values (concrete volume: 10 m³; steel content: Medium (beams, ~100 kg/m³); bar size: Y10 – Y16), it returns:
- Reinforcing steel: 1 000 kg (100 kg/m³ × 10 m³)
- In tonnes: 1.00 t
- Estimated supply & fix cost: R 30 000 (R 30/kg)
How the calculator works
It multiplies the concrete volume by a steel content in kilograms per cubic metre, which varies with the element: lightly reinforced slabs carry less steel than beams, and heavily loaded columns carry the most. The total mass is then priced at a supply-and-fix benchmark rate per kilogram. This is a budgeting rule of thumb. The engineer's bending schedule is the real quantity.
Reading bar sizes
In South Africa, bars are marked by type and diameter: Y for high-yield deformed bar and R for mild-steel round bar, followed by the diameter in millimetres. Y12 is a 12 mm high-yield bar. The mass of a bar depends only on its diameter, which is useful for checking a schedule:
- Y10: about 0.62 kg per metre
- Y12: about 0.89 kg per metre
- Y16: about 1.58 kg per metre
- Y20: about 2.47 kg per metre
- Y25: about 3.85 kg per metre
- Y32: about 6.31 kg per metre
Working from a bending schedule
When the engineer issues drawings, the bending schedule lists every bar by mark, diameter, number, length and shape, following SANS 282. Multiply each line's total length by the mass per metre for its diameter and add them up. That gives a far better figure than a kg/m³ rule. Allow a small percentage for laps and wastage if the schedule does not already include them.
Mesh reinforcement in slabs, such as Ref 193 or Ref 245, is priced per square metre rather than per kilogram. Measure the slab area and add the lap allowance the supplier recommends.
What the rate includes
A supply-and-fix rate covers the steel, cutting and bending, delivery and fixing it in the formwork with tie wire and spacers. Smaller bars cost more per kilogram to fix because there are more of them per tonne. Concrete cover, the distance between the steel and the surface, is set by the engineer for durability; on coastal and wet sites it is larger, and getting it wrong is a common cause of early concrete damage.
Questions
- How much rebar per m³ of concrete?
- As a rule of thumb: ~60 kg/m³ for lightly-reinforced slabs, ~100 kg/m³ for beams, and ~150 kg/m³ or more for heavily-loaded columns. The bending schedule is the accurate source.
- Does the cost include cutting and bending?
- Yes — the supply-and-fix rate covers steel, cutting, bending, and fixing in place. Mesh reinforcement is priced separately per m².
- Why does bar size change the rate?
- Smaller bars (Y10–Y16) cost slightly more per kg because there is more cutting, bending, and fixing labour per tonne than with larger bars.
Compiled by Setout. Figures are planning-stage estimates, not quotes.
Reviewed by Aidan Koetaan MBA PMP, quantity surveyor and construction project manager.