How to prepare a bar bending schedule: cut length, weight per metre and a worked stirrup
By Sithu, Founder · 7 min read · Last reviewed 29 October 2026
Steel is often the costliest material on a structure, and the bar bending schedule decides how much of it you buy, how it is cut, and how much of it you are paid for. A BBS that is out by a few percent is a few percent of your steel bill.
This guide walks through the columns of a BBS, the one formula you need for weight, how bends change the cut length, and a worked stirrup from a column.
What goes in a BBS
One row per bar mark, read straight from the structural drawing:
- Member (footing F1, column C3, beam B12) and bar mark
- Bar diameter and shape
- Number of members, and number of bars in each member
- Cut length of one bar
- Total length = members × bars × cut length
- Weight = total length × weight per metre for that diameter
Weight per metre: d²/162
Steel weighs about 7,850 kg per cubic metre. Work that through for a round bar and the weight in kg per metre comes out to the diameter in mm squared, divided by 162.
| Dia (mm) | kg per metre |
|---|---|
| 8 | 0.395 |
| 10 | 0.617 |
| 12 | 0.889 |
| 16 | 1.580 |
| 20 | 2.469 |
| 25 | 3.858 |
| 32 | 6.321 |
Cut length: add hooks, take off bends
A bent bar stretches on the outside of every bend, so the cut length is a little less than the sum of its straight lengths. Site practice takes off a fixed allowance for each bend and adds a length for each hook.
| Bend or hook | Allowance |
|---|---|
| 45° bend | take off 1d |
| 90° bend | take off 2d |
| 135° bend | take off 3d |
| Stirrup hook | add 10d each |
Worked example: column stirrup
a = 300 − 2 × 40 = 220 mm b = 450 − 2 × 40 = 370 mm Sides: 2 × (220 + 370) = 1,180 mm + 2 hooks: 2 × 10 × 8 = 160 mm − 3 bends at 90°: 3 × 2 × 8 = 48 mm − 2 bends at 135°: 2 × 3 × 8 = 48 mm Cut length = 1,244 mm Weight = 1.244 × 0.395 = 0.491 kg
With 30 stirrups in a column and 12 such columns, that row is 360 stirrups, 447.8 m and 176.9 kg of 8 mm steel.
Mistakes that cost steel
- Forgetting laps on bars longer than the 12 m stock length. Every lap is extra steel; count them per the drawing.
- Adding wastage inside the BBS. Keep the BBS to the drawing and add wastage when you order, so the BBS stays the figure you bill.
- Totalling by member but never by diameter. You buy steel by diameter; the summary by dia is what goes to the supplier.
- Not checking the BBS against the bill. Payment for reinforcement is usually by weight worked out from the BBS and recorded in the measurement book, so the BBS is the bill. Check what your agreement says.
Common questions
- What is the formula for steel weight per metre?
- Diameter in mm squared, divided by 162, gives kg per metre. A 12 mm bar weighs 144 / 162 = 0.889 kg per metre; a 16 mm bar weighs 1.580 kg per metre.
- How do you calculate the cut length of a stirrup?
- Add the straight sides (inside the cover), add a hook length for each hook, and take off an allowance for each bend. For a 300 × 450 column with 40 mm cover and 8 mm stirrups, using 10d hooks and 2d / 3d bend allowances, the cut length is 1,244 mm.
- What is the bend deduction for 90° and 135°?
- Most sites take off 2d for a 90° bend and 3d for a 135° bend, and 1d for 45°, where d is the bar diameter. Follow the drawing or the department's rule where it says otherwise.
- Should wastage be added in the BBS?
- No. Keep the BBS to the drawing so it matches what is measured and billed, and add wastage separately when you order steel.
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