How do you use the steel calculator?
- Choose how to estimate: from the volume of a concrete element, or from the built-up area of the house.
- Enter the size, and the steel per m³ or per sq ft. Take that figure from your structural engineer; the defaults are examples.
- Read the steel in kg and tonnes. Price, wastage and bar size are under “Adjust price, wastage and bar size”.
How is reinforcement steel estimated?
The exact quantity comes from the structural engineer’s bar bending schedule, which lists every bar by diameter, length and shape. Before that exists, builders estimate steel as kilograms per cubic metre of concrete for an element such as a slab, or kilograms per square foot of built-up area for a whole house. Both figures depend on the design, spans, loads and soil, so they should come from your engineer, not a general rule. Add an allowance for cut pieces and overlaps where bars join.
To check bar weights, a standard rule gives the weight of a steel bar in kg per metre as its diameter in millimetres squared, divided by 162. It follows from steel’s density of about 7,850 kg per m³.
How the steel is worked out
Length × width × thickness (m³) × steel per m³Built-up area × steel per sq ftStep 1 or 2 × (1 + cutting and laps %)d² ÷ 162 kg per m × bar lengthWorked example: 20 × 10 ft slab, 150 mm thick
The slab is 2.787 m³. At an example 100 kg per m³ that is 279 kg; with 5% for cutting and laps, 293 kg, or 28 bars of 12 mm, 12 m long. At ₹ 65 a kg the steel costs ₹ 19,022.
Worked example: 1,200 sq ft house by area
At an example 4 kg per sq ft, a 1,200 sq ft built-up house needs 4,800 kg, or 5,040 kg (5.04 tonnes) with 5% wastage. At ₹ 65 a kg that is ₹ 3,27,600. Your engineer’s figure may be quite different.
How much does a steel bar weigh?
| Diameter | kg per m | kg per 12 m bar |
|---|---|---|
| 8 mm | 0.395 | 4.74 |
| 10 mm | 0.617 | 7.41 |
| 12 mm | 0.889 | 10.67 |
| 16 mm | 1.580 | 18.96 |
| 20 mm | 2.469 | 29.63 |
| 25 mm | 3.858 | 46.30 |
What should you check when buying steel?
- Buy the grade and diameters your engineer specifies, and ask for the test certificate with each batch.
- Weigh a few bars on delivery against the d² ÷ 162 figure to check you are getting full-weight bars.
- Store bars off the ground and covered to keep rust down.
Frequently asked questions
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Sources
- Bar weight: d² ÷ 162 kg per m, from steel density of about 7,850 kg per m³ (standard engineering rule).
- Steel per m³ and per sq ft, bar size, price and wastage: your inputs; the defaults are examples. No market prices are assumed.
Indicative quantities for planning, not a structural design. Follow your structural engineer’s drawings and bar bending schedule. For GST, indicative only.
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