Why this calc exists
The d²/162 formula for rebar weight per metre is one of the few formulas in concrete practice that every site engineer remembers. It comes from m = ρ × π × d² / 4 = 7850 × π / 4 / 1000 = 6.162 ≈ 1/162 kg/m for a bar of diameter d in mm. The 162 is just a convenient denominator; the actual constant is 162.2.
Why it matters: rebar procurement is by mass, but BBS quantities are by length. Without a fast d²/162 calculation, you can't reconcile the two, and you'll either over-order (cost) or under-order (halting pours). The rebar weight calculator does the calc in both directions: given length, output mass; given mass, output length.
Code references (with provenance)
- IS 1786:2008 — High strength deformed steel bars and wires for concrete reinforcement. Specifies nominal mass per metre for each bar size.
- IS 2502:1963 — Bending and fixing of bars.
- IS 456 Cl 26.2 — Reinforcement (bond, development, laps); material standards per IS 1786.
d²/162 reference table
Ø 6 mm: 6²/162 = 0.222 kg/m
Ø 8 mm: 0.395 kg/m
Ø 12 mm: 0.888 kg/m
Ø 16 mm: 1.578 kg/m
Ø 20 mm: 2.466 kg/m
Ø 25 mm: 3.854 kg/m
Worked: 2,500 running metres of Ø16 mm = 2,500 × 1.578 = 3,945 kg = 3.95 tonnes.
Field notes (what trips people up)
- Order by mass, never by bar count. A 12 m Ø16 bar weighs 18.94 kg nominal; actual could be 18.6–19.2 kg depending on the manufacturer's tolerance (IS 1786 allows ±7 % on individual bars, ±5 % on a sample of 10+). For bulk procurement, use 1.578 kg/m × total length + 3 % margin.
- d²/162 is nominal. IS 1786 nominal density is 7850 kg/m³; some manufacturers are slightly over (7900–8000) for better bond. Don't be surprised if your actual mass is 1–2 % above the d²/162 number.
- Coated rebar (epoxy, galvanised) weighs 2–5 % more. The base bar weight stays d²/162; the coating adds a small mass. Check the supplier's TDS.
Worked example
Site: 5,000 m² podium slab, 80 kg/m³ typical reinforcement ratio.
Estimated steel: 5,000 × 0.25 (slab thickness) × 80 = 100 tonnes.
Total: ~97,123 running metres, ~10,000 individual bars (12 m stock).
FAQ
Why exactly 162?
From m = ρ × A × L = 7850 × π × (d/2)² / 1000 = π × 7850 / 4000 × d² = 6.162 × d² ≈ d²/0.162. The 162 is 1000/(π·7850/4) — a convenient denominator. The more precise constant is 162.2.
Is the calculator accurate for Fe415 vs Fe500?
Yes — d²/162 is purely geometric (depends on density, not yield strength). Fe415, Fe500, Fe550 all use the same nominal mass.
What about bundled bars?
Two bars in contact: equivalent single bar = d × √2. Three bars: d × √3. For BBS, just sum individual lengths (the bundle is a delivery convention, not a structural change in the steel area).
Related reading & tools
- ../calculators/rebar-weight.html — Rebar Weight calculator
- calc-bbs-cutting-length-significance.html — BBS / Cutting Length Significance
- reinforcement-steel-is1786.html — Reinforcement Steel — IS 1786 (blog)
Indicative tool — not a substitute for engineering judgement.
Results are computed from formulae and reference values cited to Indian Standards and other published codes as named on this page, using nominal default assumptions; clause and table references are given in good faith for study and preliminary checks. Always verify the current edition and amendments of any cited standard in the BIS catalogue before relying on it. Final mix proportions, structural checks and construction decisions must be confirmed by a qualified engineer against the project design brief, drawings and site conditions. ConcreteInfo accepts no liability for design, procurement or construction decisions taken on the basis of these tools. Code references & rights: Indian Standards are the property of the Bureau of Indian Standards (© BIS) — official PDFs at bis.gov.in. Shared in good faith as technical reference for the civil engineering fraternity — always verify against the official publication.