How the bar bending schedule is calculated
For each bar, the cutting length is the clear length between supports, minus concrete cover at both ends, plus allowances for hooks, minus deductions for bends:
- Hook — a standard 180° hook adds about 9 times the bar diameter (9d) per hook.
- 90° bend — deduct 2d per bend (the bar's neutral axis shortens at a bend).
- 45° bend — deduct 1d per bend.
The unit weight of a round bar is the well-known d²/162 kg per metre, where d is the diameter in mm. So a 12 mm bar weighs 144/162 = 0.889 kg/m, a 16 mm bar 1.58 kg/m, and so on. Total weight is unit weight × cutting length × number of bars, summed across the schedule and grouped by diameter for ordering.
This tool follows the standard textbook BBS method used on Indian sites. For execution, always reconcile against your structural drawings and IS 2502 bar-bending conventions — lap lengths, development lengths and complex bend shapes need detailing judgement this estimate doesn't replace.
Common bar diameters & unit weights
| Diameter | Unit weight (kg/m) |
|---|---|
| 8 mm | 0.395 |
| 10 mm | 0.617 |
| 12 mm | 0.889 |
| 16 mm | 1.580 |
| 20 mm | 2.469 |
| 25 mm | 3.858 |
Estimating steel for a whole structure? The BOQ estimator gives a quick per-element steel figure by typical kg/m³; use this BBS tool when you need the actual cut lengths and bar-wise weights.