The Rebar Weight Calculator computes the unit weight (kg/m) and total weight of TMT reinforcement bars per IS 1786:2008. It uses the standard formula W = d²/162 (d in mm) which derives from steel density 7,850 kg/m³ and circular cross-section. Enter a bar diameter, length, and number of bars — get total weight in kg, plus the IS 1786 tolerance band (±3.5%).
Use it during BBS preparation, material take-off, billing reconciliation, or as a quick reference when verifying a vendor's invoice against actual delivered weight.
Steel density: 7,850 kg/m³ ≈ 7.85 g/cm³. Cross-section area of round bar = π × d² / 4 (mm²) = π × d² / 4 × 10⁻⁶ m². Weight per metre = area × 1m × density = π × d² / 4 × 10⁻⁶ × 7,850 = d² × 6.165 × 10⁻³ ≈ d² / 162.16. The 162 figure is the rounded constant used universally in Indian practice — yields 0.395 kg/m for 8mm, 0.617 kg/m for 10mm, 0.888 kg/m for 12mm, and so on.
Per IS 1786:2008 Table 1: 6mm = 0.222 kg/m, 8mm = 0.395, 10mm = 0.617, 12mm = 0.888, 16mm = 1.578, 20mm = 2.466, 25mm = 3.852, 28mm = 4.834, 32mm = 6.313, 36mm = 7.99, 40mm = 9.864. Tolerance band is ±3.5% of nominal weight (also Table 1) — actual delivered batches may run light (vendors save material) or heavy (out-of-spec mill). Always verify against weighbridge.
BBS material take-off applies a wastage allowance: 3% for typical jobs (offcuts, tying, mill mistakes), up to 5% for heavily detailed members (columns with cranks, footings with multiple-direction reinforcement). Lap length per IS 456 Cl. 26.2.5: tension lap = 50d (Fe 415) / 60d (Fe 500); compression = 40d. Don't forget cranks at supports for slabs / cantilevers — adds ~0.42d × cover-to-cover height per crank.
12mm unit weight: 0.888 kg/m. 1,000 / 0.888 = 1,126 metres. If sold in standard 12-metre lengths, that's 1,126 / 12 = 94 bars. With 3% wastage allowance, order 97 bars (1,164 m). At ₹70/kg Fe 500D, cost = 1,000 × 70 = ₹70,000. Reverse: a 12-metre 12mm bar weighs 12 × 0.888 = 10.66 kg. A bundle of 50 bars = 533 kg.
Number is yield strength (N/mm²): Fe 415 = 415, Fe 500 = 500, Fe 550 = 550, Fe 600 = 600. Suffix D (or HCRM/HYSD) indicates high ductility. Fe 500D is the modern default for RCC — combines high yield strength with good elongation (≥ 16% per IS 1786:2008) for ductile failure under seismic load. Per IS 13920:2016, Fe 500D or Fe 415 is required in seismic zones (IV, V) for primary members.
Steel density is 7,850 kg/m³, and the constant comes from π × 7,850 / 4 / 1,000 = 162.16. Indian practice rounds to 162 for simplicity. Using 162 introduces a +0.1% error vs the exact value — within IS 1786 tolerance. ACI 318 / BS 8110 use slightly different constants because of local density assumptions and unit conventions (kg/m³ vs lb/ft³).
3% for routine jobs (slabs, beams, simple columns), 5% for complex detailing (heavily congested columns, foundation rafts with overlapping reinforcement), 7-8% for prestressed concrete (PT cables) due to anchor losses and cutting. Always verify against actual site wastage from past projects with your contractor — newer crews can run higher (8-10%).
Nominal weight = catalogue value per IS 1786 Table 1. Actual delivered weight may differ by ±3.5% per the tolerance band — vendors often supply slightly under nominal to save material. Always get a mill test certificate and verify against weighbridge for projects > ₹10 L. Discrepancy beyond -3.5% is grounds for rejection.
Yes. Per IS 13920:2016 Cl. 5.3.1, mechanical couplers (Type 1 / Type 2 per IS 16172) or full-penetration welds can replace lap splices in seismic zones, saving steel and avoiding congestion. Couplers especially useful for #8 (25mm) and larger bars where laps become impractical (50d × 25 = 1,250 mm). Cost: coupler ₹100-180 each vs lap material; weld ₹50-90 each but needs WQT / WPS.