Labs · Rebar estimator
How much steel does my building need, and in which bar sizes?
For a 4-storey housing block of 250 m² per floor, allow about 40 tonnes of reinforcement (range 29 to 53 t), before structural design.
Result
Illustrative—t
Estimated reinforcement (central value)
—t
Indicative range
—m²
Gross floor area
Assumptions behind the estimate
| Assumption | Central value | Range | Status | Source |
|---|---|---|---|---|
| Reinforcement per m² of floor: Housing | 38 kg/m² | 28 – 50 kg/m² | Assumption | Cameroon Steel Labs planning assumption for a reinforced-concrete frame: reinforcement ratio of 80 to 110 kg per m³ of concrete × 0.35 to 0.45 m³ of concrete per m² of floor. Indicative; structural design sets the real value. |
| Reinforcement per m² of floor: Offices | 46 kg/m² | 35 – 60 kg/m² | Assumption | Cameroon Steel Labs planning assumption for a reinforced-concrete frame: reinforcement ratio of 100 to 130 kg per m³ of concrete × 0.35 to 0.46 m³ of concrete per m² of floor. Indicative; structural design sets the real value. |
| Reinforcement per m² of floor: Industrial | 55 kg/m² | 40 – 75 kg/m² | Assumption | Cameroon Steel Labs planning assumption for a reinforced-concrete frame: reinforcement ratio of 100 to 150 kg per m³ of concrete × 0.40 to 0.50 m³ of concrete per m² of floor. Indicative; structural design sets the real value. |
| Share of the mass by bar diameter | Ø8: 16%; Ø10: 18%; Ø12: 22%; Ø14: 12%; Ø16: 14%; Ø20: 10%; Ø25: 6%; Ø32: 2% | — | Illustrative | Cameroon Steel Labs illustrative assumption, typical of a mid-rise reinforced-concrete frame; to be replaced by the project’s bar schedule. |
| Offcuts and laps (adjustable) | 5% | 0 – 15% | Assumption | Cameroon Steel Labs site assumption; depends on the lengths ordered and on the bending schedule |
| Density of steel | 7,850 kg/m³ | — | Sourced | EN 10080:2005, nominal mass basis: m = π/4 · d² · 7,850 kg/m³ = 0.006165 · d² kg/m |
How this is calculated
Nominal mass per metre: m = 0.006165 · d² kg/m (d in mm), derived from the density of steel (7,850 kg/m³).
Reinforcement per m² of floor. For each building type, the range is the product of two planning assumptions given in the table: a reinforcement ratio (kg of steel per m³ of concrete) and a volume of concrete per m² of floor. The low end multiplies the two low values, the high end the two high values; the central value lies between them. Across the three types the assumptions run from 80 to 150 kg/m³ and from 0.35 to 0.50 m³/m², that is 28 to 75 kg per m²: every value the tool uses lies inside. The split by diameter, shown in the same table, is typical of a mid-rise building.
Calculation. Mass = floor area × reinforcement per m² × (1 + offcuts and laps); by diameter: mass × share of the diameter; number of bars = mass ÷ (mass per metre × bar length), rounded up.
Limit: this tool helps with budgets and purchase planning; it never replaces an engineer’s structural design.
Sources
- EN 10080:2005 and BS 4449:2005+A3:2016: nominal mass and tolerances of reinforcing steel
- Cameroon Steel, Labs method note (derived: steel density 7,850 kg/m³; assumed: planning intensities and split by diameter, shown in the table)