Reinforcement Steel Quantity Estimator
Quick rebar take-off for slabs and members, with the IS 456 limits checked.
Take-off
Slab
Members
Steel by volume: 1 % = 78.5 kg per m³. Enter your design's figure — the checks compare it with the IS 456 limits for main bars.
Price optional
Bars
IS 456 checks
Results are estimates from the formulas shown, not a professional design or certification. Have a qualified engineer verify anything safety-critical (structures, electrical installations, gas or pressure systems).
About the Reinforcement Steel Quantity Estimator
Estimate reinforcing steel in two ways. Slab mesh lays bars both ways at the spacings you give, inside the cover, with optional hooks or bends at the ends, every other main bar cranked over the supports and IS 456 laps where a bar is longer than a stock bar — and tells you how many bars of what length you need. Members by steel % takes the concrete volume of beams, columns, footings and slabs and the steel as a percentage (or kg per m³) for a fast take-off.
Both give the steel by diameter in kg and tonnes, kg per m² and per m³ of concrete and the cost at your price. The results are checked against the IS 456 rules: at least 0.12 % (HYSD) or 0.15 % (mild steel) in each direction of a slab, bars no larger than D/8, maximum spacings, 0.8–6 % in columns and at most 4 % tension steel in beams.
How to use it
- Pick Slab mesh or Members by steel %, and the steel grade (it sets the minimum steel and the lap length).
- For a slab, enter its size out to out, thickness and cover, then the bar size and spacing each way, which bars are main, the number of layers and any hooks, bends or cranks.
- For members, add each beam, column or footing with its size (or volume), how many there are and the steel as % of the concrete or kg per m³.
- Read the bar counts, lengths and weights, the IS 456 checks and the cost; copy the result or download it as CSV.
Examples
22 bars of 4,190 mm along the length (11 cranked, + 62 mm each) = 92.86 m = 57.30 kg · 21 bars of 3,190 mm = 66.99 m = 26.46 kg · total 83.76 kg = 6.13 kg/m² = 49.0 kg/m³
10 mm @ 150 = 524 mm²/m = 0.419 % ≥ 0.12 % · 8 mm @ 200 = 252 mm²/m = 0.201 % · bars ≤ 125/8 = 15.6 mm · spacings within 300 mm
0.414 m³ × 1.5 % × 7,850 kg/m³ = 48.75 kg (117.75 kg/m³)
How the slab mesh is counted
Bars along the length are as long as the slab less a cover at each end, and spread across its width less two covers: number = (width − 2 × cover) ÷ spacing, rounded down, plus one — and the same the other way. End hooks or 90° bends add the IS 2502 Table II allowances (for example 130 mm per hook and 75 mm per bend on a 10 mm TMT bar). A cranked bar rises from the bottom layer to the top layer, a height of D − 2 × cover − bar diameter, and each 45° crank adds that height × tan 22.5° = 0.414 × height. With top and bottom layers, the cranked bars are counted in the bottom layer only.
Bars longer than the stock length (12 m unless you change it) get IS 456 laps of the larger of Ld and 30φ, where Ld = φ × 0.87 fy ÷ 4τbd. Bars over 32 mm are not lapped (IS 456 Amendment 3); they need couplers. Lengths here are exact; a bar bending schedule then rounds each cutting length up to 25 mm.
Members by steel percentage
Steel weight = concrete volume × steel percentage × 7,850 kg/m³, so 1 % of the concrete volume is 78.5 kg of steel per m³. If you know a kg/m³ figure from a similar structure, enter that instead; switching a member between % and kg per m³ converts the figure, so the weight does not change. The percentage you enter is an assumption about your design — the structural drawings decide the real figure — so use this mode for early estimates and the bar bending schedule for the final quantity.
IS 456 limits checked
- Slabs (cl. 26.5.2.1): at least 0.15 % of the gross section in each direction for mild steel, 0.12 % for HYSD bars or welded fabric — with top and bottom meshes, the bars of both layers count. Cl. 26.5.2.2: bars no larger than one-eighth of the slab thickness.
- Spacing in slabs (cl. 26.3.3(b)): main bars at most 3 × effective depth or 300 mm; distribution bars at most 5 × effective depth or 300 mm (Amendment 3 changed 450 mm to 300 mm).
- Columns (cl. 26.5.3.1): longitudinal steel 0.8 % to 6 % of the gross section; where bars are lapped, usually not more than 4 %.
- Beams (cl. 26.5.1.1): tension steel at least 0.85 bd/fy and at most 0.04 bD; compression steel also at most 0.04 bD (cl. 26.5.1.2).
- Footings (cl. 34.5.1): minimum steel and spacing as for solid slabs.
Sources
- IS 456:2000, Plain and Reinforced Concrete — Code of Practice (with Amendments 1–3): cl. 26.2.1, 26.2.5.1, 26.3.3, 26.5.1.1, 26.5.1.2, 26.5.2, 26.5.3.1 and 34.5 — archive.org
- IS 2502:1963, Table II hook and bend allowances — archive.org
- IS 1786:2008 (with Amendment 1), Table 1 nominal masses and areas — archive.org
Limitations
- A take-off, not a design: bar sizes, spacings, extra top bars over supports, laps and anchorage come from the structural drawings.
- The slab mesh assumes one rectangular panel with bars stopping at the cover; openings, chairs, extra bars at openings and top steel over beams are not included.
- In the percentage mode the result is only as good as the percentage you assume; the checks compare it with the code limits for main bars, not with your actual design.
- Weights are nominal (IS 1786); delivered steel varies within the standard's mass tolerance.
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Frequently asked questions
How much steel is in 1 m³ of concrete?
It depends entirely on the design. As a conversion, 1 % steel by volume is 78.5 kg per m³. The 125 mm slab in the example, with 10 mm bars at 150 mm and 8 mm at 200 mm, works out at about 49 kg per m³ (6.1 kg per m² of slab).
What is the minimum steel in a slab?
IS 456 cl. 26.5.2.1: 0.12 % of the gross section in each direction for HYSD (TMT) bars, 0.15 % for mild steel. For a 125 mm slab that is 150 mm² per metre width — 8 mm bars at up to 335 mm, though the distribution bars may not be further apart than 300 mm.
How many bars are needed in a slab?
Across each side, (length − 2 × cover) ÷ spacing, rounded down, plus one. A slab 3.23 m wide with 20 mm cover and bars at 150 mm needs 3,190 ÷ 150 = 21.3 → 21 + 1 = 22 bars.
What are the steel limits for columns and beams?
Columns: longitudinal steel from 0.8 % to 6 % of the gross area (IS 456 cl. 26.5.3.1), usually not more than 4 % where bars are lapped. Beams: tension steel at least 0.85 bd/fy — about 0.17 % of bd for Fe 500 — and not more than 0.04 bD.
Why does this differ from my bar bending schedule?
This estimator uses exact lengths and a simple layout. A BBS follows the drawings bar by bar, rounds every cutting length up to the next 25 mm (IS 2502) and includes extra bars, chairs and laps where the drawings place them, so it is usually a little higher.