Measuring reinforcement: BBS weight vs. theoretical weight
How reinforcement is measured for an RA bill: bar bending schedule lengths, sectional weight per metre, weighed steel, laps, and reconciling issued steel.
- Published
- 5 Nov 2026
- Reading time
- 4 min
- Topic
- Site to office
- Written by
- The Tatha Vastu billing team
Reinforcement is usually the largest single amount on a building RA bill, and one of the most argued. The contractor buys steel by weight off a weighbridge slip. The client usually pays for it by weight worked out from lengths on a bar bending schedule. Those two numbers are never the same, and the difference is real money.
Two ways to arrive at a weight
Theoretical weight is worked out from the bar bending schedule (BBS): the cut length of each bar times the number of bars, converted to weight at a standard sectional weight per metre for its diameter. Weighed weight is what the steel weighs on a scale. Bars are rolled within a tolerance on their mass per metre, so a bundle can weigh less or more than its theoretical weight.
Your contract decides which one is paid. Many item-rate contracts in India pay reinforcement on theoretical weight from the sectional weights, and do not pay for wastage, rolling margin or binding wire separately. Some pay on weighed weight. Read the item description and the measurement clause before the first bill goes out.
Sectional weight per metre
The weight of a steel bar per metre length is its cross-section area times the density of steel. For a bar of diameter d in millimetres, that works out to d squared divided by 162, in kg per metre.
| Diameter | Computation | kg per metre |
|---|---|---|
| 8 mm | 64 / 162 | 0.395 |
| 10 mm | 100 / 162 | 0.617 |
| 12 mm | 144 / 162 | 0.889 |
| 16 mm | 256 / 162 | 1.580 |
| 20 mm | 400 / 162 | 2.469 |
| 25 mm | 625 / 162 | 3.858 |
| 32 mm | 1,024 / 162 | 6.321 |
Use the sectional weights your contract names. If it names none, agree the table with the engineer at the start and print it on the measurement sheet, so every bill uses the same figures.
A worked BBS example
Three bar marks from one slab and four beams, measured for one RA bill.
| Bar mark | Dia | Nos x cut length | Total length | kg/m | Weight |
|---|---|---|---|---|---|
| Slab S3, bottom | 12 mm | 48 x 6.20 m | 297.60 m | 0.889 | 264.57 kg |
| Beams B7 to B10, main | 16 mm | 16 x 6.65 m | 106.40 m | 1.580 | 168.11 kg |
| Beams B7 to B10, stirrups | 8 mm | 128 x 1.42 m | 181.76 m | 0.395 | 71.80 kg |
| Total | 504.48 kg |
The arithmetic: 297.60 m times 0.889 is 264.57 kg; 106.40 m times 1.580 is 168.11 kg; 181.76 m times 0.395 is 71.80 kg. Together, 504.48 kg.
Suppose the same bars weighed 492.10 kg on the site scale. That is 12.38 kg, about 2.45%, below theoretical. On a contract that pays theoretical weight at ₹78.40 per kg, the contractor is paid ₹970.59 more than a contract paying weighed weight would pay. On a contract that issues steel to the contractor by weighed weight and recovers excess consumption, the same gap works in reverse at reconciliation.
Cut length, bends and hooks
Cut length is the length of straight bar cut before bending. It is not the sum of the dimensions on the drawing: bends and hooks change it. BBS practice adds hook allowances and deducts bend allowances by diameter. Use the allowances your contract, drawings or the engineer specify, and apply them consistently, because a change in convention halfway through a contract shows up as a step in cumulative weight.
Laps, chairs and wastage
- Laps shown on the drawings, or approved by the engineer, are usually measured and paid. Laps added because bars were cut short for convenience usually are not.
- Chairs and spacer bars are paid or not as the contract says. Some contracts measure them as reinforcement; others include them in the rate.
- Binding wire is commonly included in the rate and not measured.
- Cutting wastage is not paid on a theoretical-weight contract. It is the contractor's cost, priced into the rate.
Client-issued steel
Where the client issues steel, the contract normally reconciles quantity issued against theoretical consumption, with a permitted allowance for wastage. Steel used above that allowance, or not returned, is recovered at the rate the contract sets, often a penal one. Keep the issue register by diameter, and reconcile every month against the BBS weight billed. The cement and steel reconciliation template sets this out.
What the engineer checks
Reinforcement is checked before concrete is poured, and that is the moment to record it. Once the slab is cast, nobody can count the bars again. A billing claim for steel is strongest when the BBS, the pre-pour checklist signed by the engineer and a photograph of the cage all carry the same date and location.
- The BBS is based on the current revision of the structural drawing.
- Bar marks on the BBS match the bars in place, by diameter and spacing.
- Laps are where the drawing shows them, and only those laps are measured.
- The weight on the bill matches the BBS, at the agreed sectional weights.
kg and MT
BOQs often list reinforcement in kg; purchase and issue registers often keep it in MT. On RA Bill No. 7 for a ward office building, item 4.1 bills 9,745 kg of Fe 500D at ₹78.40 per kg, ₹7,64,008. Keep one unit through the measurement record and convert only for display.
How Tatha Vastu measures reinforcement
In the measurement book, reinforcement is recorded from the BBS: bar mark, diameter, number and cut length, with the sectional weight table set once per work order. Weight rolls into the abstract in the BOQ's unit, and the BBS weight sheet template exports the same figures. Client-issued steel is reconciled against billed weight on every bill.