Cut length of a bar after bending — outside legs plus hook allowances minus bend deductions.
Site-practice bend deductions on outside dimensions (90° → 2d; a 135° hook allowance is its extension + 3d, bent round a 4d pin). Stirrup hooks: IS 13920:2016 — 6d ≥ 65 mm (hoop definition, Cl 3 — seismic hoops). Confirm these constants against your own site standard.
Reference only. Cutting lengths use common site-practice bend deductions on outside dimensions (90° → 2d; 135° hook allowance = extension + 3d), so the hook extension survives bending; stirrup 135° hooks per IS 13920:2016 (6d ≥ 65 mm) or 10d ≥ 75 mm practice, L-bar hooks max(9d, 75 mm). Deductions vary with bending equipment, mandrel diameter and house standards — always confirm against your approved bar-bending schedule before cutting. Need the full schedule for a whole member? Generate a Bar Bending Schedule in Section Design.
How the BBS Cutting Length Calculator works
A bar is measured on the drawing by its bent dimensions, but it has to be cut straight. When a bar is bent, the outside of the bend stretches, so adding up the segment lengths overstates the steel needed. The cutting length is the sum of the segments plus any hooks, minus a bend deduction for each bend. This calculator uses common site practice on outside dimensions: a 90° bend deducts 2d and a 135° hook adds its extension plus 3d, where d is the bar diameter (both are the geometry of a bend round a 4d pin). These are site-practice figures, not IS 2502 tables.
Three shapes are covered. A straight bar is cut to its length. An L-bar is leg 1 plus leg 2 minus one 90° deduction of 2d, with an option to add an end hook of max(9d, 75 mm) at both ends. A stirrup is a two-legged closed rectangular link with two 135° hooks.
For the stirrup, the outside width and depth are the member size less twice the clear cover. The outside perimeter 2(A + B) is reduced by three 90° bend deductions and increased by two 135° hook allowances (extension + 3d), so the hooks keep their full extension after bending. The popular 2(a + b) + 2h − 3 × 2d − 2 × 3d on centre-line sides deducts the bends twice and leaves hooks only about 2d long. The hook extension is either 6d but not less than 65 mm (IS 13920:2016, the default) or 10d but not less than 75 mm (the superseded IS 13920:1993 rule that is still common site practice).
The result is shown in millimetres, with the value in metres and the length rounded up to the next 10 mm for cutting on site. The page reports an error instead of a number if a field is blank or the cover is too large for the member.
- Bend deduction / hook allowance
- 90° → −2d; 135° hook → h + 3d
- L-bar
- CL = leg1 + leg2 − 2d (+ 2 × max(9d, 75) with end hooks)
- Stirrup outside sides
- A = B − 2c, B′ = D − 2c
- Stirrup hook extension
- h = max(6d, 65 mm) or max(10d, 75 mm)
- Stirrup cutting length
- CL = 2(A + B′) − 3 × 2d + 2 × (h + 3d)
Follows: Site-practice bend deductions (bend round a 4d pin) · IS 13920:2016 Cl 3 (hoop definition, 135° hook extension)
Worked example: cutting length of an 8 mm stirrup for a 230 × 450 mm beam
Given
- Beam width B = 230 mm, overall depth D = 450 mm
- Clear cover c = 25 mm
- Stirrup bar d = 8 mm
- Hook rule: IS 13920:2016, 6d but not less than 65 mm
Steps
- Outside width: A = 230 − 2 × 25 = 180 mm.
- Outside depth: B′ = 450 − 2 × 25 = 400 mm.
- Outside perimeter: 2 × (180 + 400) = 1160 mm.
- Three 90° bends: 3 × 2 × 8 = 48 mm deducted.
- Hook extension: max(6 × 8, 65) = max(48, 65) = 65 mm; each 135° hook allowance is 65 + 3 × 8 = 89 mm, so two hooks add 178 mm.
- Cutting length: 1160 − 48 + 178 = 1290 mm.
Result: Cut each stirrup to 1290 mm (1.290 m).
Enter the same values in the calculator above to check each step.
Frequently asked questions
How is the cutting length of a stirrup calculated?
Take the outside perimeter of the stirrup, subtract three 90° bends at 2d each and add two 135° hook allowances of the extension plus 3d. For an 8 mm stirrup in a 230 × 450 mm beam with 25 mm cover and 65 mm hooks, that is 1160 − 48 + 2 × 89 = 1290 mm. The often-quoted 1162 mm deducts the bends twice; bent up, its hooks come out about 3 mm long instead of 65 mm.
What is the bend deduction for 45°, 90° and 135° bends?
Common site practice deducts about 1d for a 45° bend, 2d for a 90° bend and 3d for a 135° bend from the outside leg dimensions, where d is the bar diameter (2d is the geometry of a bend round a 4d pin). For a 12 mm bar a 90° bend therefore takes 24 mm off the sum of the outside leg lengths. A hook allowance measured from the outside of its bend already includes the bend, so it is not deducted again.
What is the hook length for a stirrup as per IS 13920?
IS 13920:2016 defines the 135° hook extension of a hoop as 6d but not less than 65 mm, so 8 mm and 10 mm stirrups both get 65 mm. The older IS 13920:1993 rule of 10d but not less than 75 mm is still common on site; with it the same 8 mm stirrup comes out at 1320 mm instead of 1290 mm.
How do I find the cutting length of an L-shaped bar?
Add the two leg lengths and subtract one 90° bend deduction of 2d. A 12 mm bar with legs of 1000 mm and 500 mm is cut to 1000 + 500 − 24 = 1476 mm. If you add a hook of max(9d, 75 mm) at both ends, each hook adds 108 mm and the cutting length becomes 1692 mm.
What does this calculator not account for?
It handles one bar at a time in three shapes only: straight, L-bar and rectangular two-legged stirrup. It does not cover cranked bars, multi-legged or circular links, laps or wastage, and the deductions do not change with mandrel diameter or bending machine. Check the constants against your approved bar bending schedule before cutting.
Step-by-step guides
- BBS of Slab: Bar Bending Schedule for a Slab with Worked ExampleHow to prepare the bar bending schedule of an RCC slab: bar spacing, number of bars, cutting lengths, bend deductions and steel weight, with a 3 m × 4 m slab.
- Steel Weight Formula D²/162: Rebar Weight per Metre with TableHow to calculate the weight of a steel bar with D²/162: where 162 comes from, a kg/m table for 6 to 40 mm bars, and worked examples for 12 mm bars.
- Development & Lap Length (IS 456) — Formula & ExampleHow to calculate development length (Ld) and lap length to IS 456:2000 Cl 26.2, with a ready Ld/φ table for Fe 415, Fe 500 and Fe 550 and a worked example for a 16 mm bar.
- Stirrup Cutting Length (IS 2502) — BBS FormulaCalculate the cutting length of a rectangular stirrup step by step: outside dimensions, 135° hooks per IS 13920 and the IS 2502 bend allowances, with a worked 230 × 450 mm beam example.
Related tools
- Steel Weight CalculatorConvert the total cut length into kilograms and tonnes.
- Development Length CalculatorFind the anchorage and lap lengths to add to straight bars.
- Section DesignGenerate a full bar bending schedule for a designed member.
- Rebar CalculatorChoose the bar size and spacing before scheduling the bars.