Last reviewed 16 Sept 2026 · 7 min read
Bar bending schedule (BBS)
A bar bending schedule is a detailed list of all reinforcement bars in a structural element (or project), giving their mark, shape, diameter, number, cutting length and weight.
Purposes
- Accurate quantity of steel for estimation, procurement and billing.
- Instructions for cutting and bending bars in the yard — reduces wastage and errors.
- Better quality control — verification of reinforcement against drawings before concreting.
- Planning of bar lengths (standard 12 m lengths) to minimise offcuts.
- Basis for measurement of reinforcement (kg/tonne) in the Measurement Book.
Format of a BBS
| Column | Content |
|---|---|
| Member / location | e.g. beam B1, slab S2, column C3 |
| Bar mark | Identification of each bar type |
| Shape (sketch) | Straight, hooked, cranked, stirrup etc. with dimensions |
| Diameter (mm) | |
| Number of members | |
| Number of bars per member | |
| Total number of bars | |
| Cutting length (m) | |
| Total length (m) | |
| Unit weight (kg/m) | |
| Total weight (kg) |
Relevant references include IS 2502 (code of practice for bending and fixing of bars) and SP 34 (handbook on concrete reinforcement and detailing).
Unit weight of bars
( in mm)
| Diameter (mm) | 6 | 8 | 10 | 12 | 16 | 20 | 25 | 32 |
|---|---|---|---|---|---|---|---|---|
| Weight (kg/m) | 0.222 | 0.395 | 0.617 | 0.889 | 1.580 | 2.469 | 3.858 | 6.321 |
Hooks, bends and allowances
Code requirements (IS 456)
- Anchorage value of a standard U-type (180°) hook is taken as 16Ø and of a 90° bend as 8Ø (with limits on bend radius) in calculating development length.
- Minimum cover and bend radii follow code provisions; stirrups in seismic detailing (IS 13920) use 135° hooks with specified extensions.
Typical site practice for cutting lengths
When a bar is bent, its measured outer dimensions exceed its centre-line length, so an allowance (bend deduction) is subtracted from the sum of the outer dimensions. Commonly used practical values are:
| Bend angle | Deduction (approx.) |
|---|---|
| 45° | 1Ø |
| 90° | 2Ø |
| 135° | 3Ø |
| 180° | 4Ø |
Hook length additions commonly adopted: about 9Ø for a 180° hook on main bars; about 10Ø (or a minimum length) for 135° stirrup hooks. These are practical approximations; exact values depend on bend radius and project specifications.
Development and lap lengths
= bar diameter; = stress in bar at the section (0.87 f_y at limit state); = design bond stress.
- Design bond stress for plain bars in tension: M20 — 1.2, M25 — 1.4, M30 — 1.5, M35 — 1.7, M40 and above — 1.9 N/mm².
- For deformed bars, increase by 60%; for bars in compression, increase by 25%.
Lap lengths (IS 456, typical):
- Tension laps: not less than or 30Ø, whichever is greater (more at critical locations).
- Compression laps: not less than the development length in compression or 24Ø, whichever is greater.
- Laps are staggered and avoided at points of maximum stress.
Cutting length formulas
Straight bar (no hooks): member length 2 × end cover
Straight bar with two 180° hooks: member length 2 × end cover (practical hook allowance) bend deductions as applicable
Cranked (bent-up) bar with 45° cranks: Extra length per crank (commonly taken as ) = vertical distance between the centres of the horizontal portions (approximately) straight length (number of cranks × ) bend deductions (if applied)
Rectangular stirrup (two 135° hooks): Centre-line dimensions: , ( = clear cover to stirrup)
Circular tie/ring: centre-line diameter + overlap/hooks
Number of stirrups: (rounded up)
Number of bars in a slab: