BBS calculator
| Bar mark | Dia | No. of bars | Cutting length (m) | Weight |
|---|---|---|---|---|
Uses IS 1786 nominal mass per metre for standard diameters. Example: B1 12 mm × 40 × 6.2 m = 248 m × 0.888 = 220.2 kg; B2 10 mm × 60 × 4.5 m = 166.6 kg; S1 8 mm × 120 × 1.1 m = 52.1 kg. Total 439.0 kg.
What is a bar bending schedule?
A bar bending schedule (BBS) lists every reinforcement bar in a member: bar mark, diameter, shape, number of bars, cutting length and weight. Site teams use it to cut and bend steel, and the total weight by diameter is what you order, issue and reconcile. Steel weight per metre is D²/162 kg, where D is the bar diameter in mm.
Steel weight formula: why D²/162
Derivation: area = πD²/4 mm² → × 1 m length × 7,850 kg/m³
= D² × π × 7,850 ÷ 4,000,000 = D² ÷ 162.2
Steel density is 7,850 kg/m³, so the exact constant is 162.2. D²/162 reads about 0.1–0.2% higher than the IS 1786 nominal masses, which is close enough for site use but not for billing. For bills and reconciliation, use the nominal masses below.
| Diameter | IS 1786 nominal mass (kg/m) | D²/162 |
|---|---|---|
| 6 mm | 0.222 | 0.222 |
| 8 mm | 0.395 | 0.395 |
| 10 mm | 0.617 | 0.617 |
| 12 mm | 0.888 | 0.889 |
| 16 mm | 1.58 | 1.580 |
| 20 mm | 2.47 | 2.469 |
| 25 mm | 3.85 | 3.858 |
| 28 mm | 4.83 | 4.840 |
| 32 mm | 6.31 | 6.321 |
| 36 mm | 7.99 | 8.000 |
| 40 mm | 9.86 | 9.877 |
Nominal masses as commonly reproduced from IS 1786 (see rebar weight chart). Check your supplier's test certificate for the actual mass.
Cutting length helper
Cutting length = total of straight segments + hook allowances − bend deductions. Bend deductions are site practice, not code, so the defaults below are editable.
Default example: an 8 mm stirrup with 1,300 mm of straight legs, three 90° bends, two 135° bends and two hooks. Sources disagree on 135° and 180° deductions and on stirrup hooks; seismic detailing (IS 13920) has its own hook rules. Use your structural drawings and project specification.
Code values vs site practice
| Item | Value | Status |
|---|---|---|
| Weight per metre | IS 1786 nominal mass; D²/162 as a quick check | Code (IS 1786) / formula |
| Development length | Ld = φ × 0.87 fy ÷ (4 τbd), with τbd raised 60% for deformed bars | Code (IS 456, cl. 26.2.1) |
| Anchorage value of bends and hooks | 4φ per 45° bend (max 16φ); 16φ for a standard U-hook | Code (IS 456, anchorage) |
| Bend deductions for cutting length | 45° = 1d, 90° = 2d, 135° = 3d | Site practice |
| Hook allowance | 9d (or 75 mm minimum, often) | Site practice |
| Lap length "50d" | Common site rule; follow the drawing and IS 456 lap rules | Site practice |
Many blogs mix up IS 456 anchorage values with cutting-length deductions. They are different things: anchorage is how much bond a bend provides; deductions correct for the bar stretching around a bend.
Development length: "47d" isn't right for every grade
Using Ld = φ × 0.87 fy ÷ (4 τbd), with design bond stress for deformed bars of 1.92 N/mm² (M20) and 2.24 N/mm² (M25):
| Steel / concrete | Development length (tension) |
|---|---|
| Fe415 / M20 | 47.0 φ |
| Fe500 / M20 | 56.6 φ |
| Fe500 / M25 | 48.5 φ |
Worked from the IS 456 formula. The widely quoted "47d" only holds for Fe415 in M20. Check against IS 456 and your design.
BBS format
| Member | Bar mark | Shape | Dia (mm) | No. of bars | Spacing | Cutting length (m) | Total length (m) | Unit wt (kg/m) | Total wt (kg) |
|---|---|---|---|---|---|---|---|---|---|
| Slab S1 | B1 | Straight | 12 | 40 | 150 | 6.20 | 248.0 | 0.888 | 220.2 |
Shape codes follow IS 2502. Group the totals by diameter at the bottom; that's the figure for ordering and reconciliation.
From BBS to steel reconciliation
The BBS gives the theoretical steel for each diameter. Compare it with the steel actually issued, diameter by diameter. In CPWD-pattern contracts, Schedule F typically allows about ±2% per diameter on department-issued steel, with recovery beyond that at the tender's rates. See the material reconciliation statement.
In True Site Sync, BBS entries sit with the measurement sheets, the BBS report totals weight by diameter, and the steel reconciliation report compares that theoretical weight with steel issued. See measurement book software.
Frequently asked questions
What is the formula for steel weight per metre?
Weight per metre in kg = D² ÷ 162, where D is the bar diameter in mm. It comes from steel density of 7,850 kg/m³. For billing, use the IS 1786 nominal mass, for example 0.888 kg/m for 12 mm.
How do you calculate a bar bending schedule?
For each bar mark, multiply the number of bars by the cutting length to get total length, then multiply by the weight per metre for that diameter. Add the weights by diameter for the order and reconciliation totals.
What is the cutting length formula for a stirrup?
Cutting length = total of straight legs + hook allowances − bend deductions. Common site practice deducts 2d per 90° bend and 3d per 135° bend and adds about 9d per hook, but follow your drawings and specification.
Is development length always 47d?
No. Using the IS 456 formula, it is about 47φ for Fe415 in M20, 56.6φ for Fe500 in M20 and 48.5φ for Fe500 in M25.
What is the weight of a 12 mm bar per metre?
0.888 kg per metre (IS 1786 nominal mass). A 12 m length of 12 mm bar weighs about 10.66 kg.
Why reconcile BBS weight with steel issued?
The BBS is the theoretical steel. Comparing it diameter by diameter with steel issued shows wastage or theft. CPWD-pattern contracts typically allow about ±2% per diameter on issued steel.
Sariya ka weight kaise nikale?
Diameter ka square ÷ 162 = kg prati meter. Jaise 12 mm sariya: 144 ÷ 162 ≈ 0.888 kg/m. Isko total length (nos × cutting length) se guna karein.
BBS, measurement and steel reconciliation in one place
Enter BBS with your measurements and see theoretical steel against steel issued, diameter by diameter.
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