What is a Bar Bending Schedule?
A Bar Bending Schedule (BBS) lists every reinforcement bar mark in a structure — its shape, cutting length, diameter, number of bars and total weight. Site engineers use it to place a precise steel order (instead of guessing from drawings) and it's the main defence against cutting wastage, which typically runs 3–5% without one.
The cutting length formula
A bar's cutting length is shorter than the sum of its straight segments, because a bend takes up less steel than the two straight legs it replaces. Standard practice (SP 34 / IS 2502) uses a deduction per bend, by angle, and an allowance for any hook:
| Bend / hook | Deduction or allowance |
|---|---|
| 45° bend | − 1d |
| 90° bend | − 2d |
| 135° bend | − 3d |
| Standard hook (135°, min. 4d extension) | + 9d |
d is the bar diameter. So for a bar with segments A and B joined by one 90° bend and a hook at each free end: cutting length = A + B − 2d + 18d.
Worked example — a 12 mm L-bend
Two segments of 1 m each, one 90° bend, no hooks, 12 mm bar: cutting length = 1000 + 1000 − (2 × 12) = 1976 mm. Weight = 1.976 m × (12²/162) = 1.976 × 0.889 ≈ 1.76 kg per bar.
Stirrup / tie cutting length
A rectangular stirrup's leg size is the member size minus cover on each face (leg width = member width − 2×cover, leg depth = member depth − 2×cover). Its cutting length is then 2×(leg width + leg depth), minus four 90° corner-bend deductions, plus two 135° hook allowances at the free ends — the "Stirrup / tie" tab above does this automatically.
Frequently asked questions
What is a Bar Bending Schedule (BBS)?
A BBS lists every reinforcement bar in a structure by shape, cutting length (including bend deductions and hook allowances), diameter, number and total weight. It converts a drawing into a purchasable steel order and is the main check against wastage.
What is the formula for cutting length?
Cutting length = sum of straight segment lengths − bend deductions + hook allowances. Bend deduction is 1d for a 45° bend, 2d for a 90° bend and 3d for a 135° bend (d = bar diameter). A standard hook adds about 9d.
How do you calculate stirrup cutting length?
Stirrup leg size = member width/depth − 2×clear cover on each side. Cutting length = 2×(leg width + leg depth) − 4×(90° bend deduction) + 2×(135° hook allowance).
How do you convert cutting length to weight?
Weight (kg) = cutting length (m) × d²/162, where d is the bar diameter in millimetres — the standard unit-weight formula for round steel bars.