Enter TMT bar diameters and lengths to get exact weight per IS 1786:2008 — the same unit weight formula used in Rebota's BBS Calculator.
Steel is typically the single largest material cost line on a structural project. The IS 1786:2008 unit weight formula (d² ÷ 162.28 kg/m, where d is the bar diameter in mm) is the definitive method for converting bar length to weight — any deviation from this formula in your estimation compounds across every bar on the project. The most common source of loss is cutting wastage from unoptimised cutting patterns, where offcuts too short to reuse are discarded rather than allocated to shorter bar requirements elsewhere in the BBS.
A slab requiring 500m of 12mm bar and 300m of 16mm bar: 12mm weight = 144 / 162.28 = 0.887 kg/m x 500m = 444 kg. 16mm weight = 256 / 162.28 = 1.578 kg/m x 300m = 473 kg. Total = 917 kg before wastage. At 3% wastage and Rs 68/kg, total cost is approximately Rs 64,222 versus Rs 62,351 without wastage — a Rs 1,871 difference that scales significantly across a full project.
Top-performing sites use cutting-length optimisation (bin-packing algorithms) when preparing the BBS, matching offcuts from longer bar requirements to shorter ones elsewhere in the schedule. This typically reduces wastage from the unoptimised 5-8% range down to 2-3%.
Structural estimators prepare the BBS first, group bars by diameter, and run cutting-length optimisation before finalising the Purchase Order — rather than ordering a flat percentage buffer on top of the theoretical weight.
Rebota's BBS Calculator implements the same IS 1786:2008 formula with First-Fit-Decreasing cutting optimisation built in, automatically minimising offcut waste and generating a ready-to-order steel schedule by diameter.
