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BBS / Cutting Length Calculator — IS 2502 Significance

Translating bar shape drawings into metre-of-bar per element — with the bend-deduction and hook allowances that IS 2502 specifies per bend angle.

Why this calc exists

Bar Bending Schedule (BBS) is the contract document that ties design drawings to procurement. Every kg of steel on site started as a line in a BBS. Get the cutting lengths right and you order exactly what you need. Get them wrong and you're either returning 10 t of offcut or halting a pour while emergency steel is sourced.

IS 2502:1963 (reaffirmed 2021) gives the rules — bend deductions per angle, hook allowances for 90°/135°/180°, plus the 2d-to-12d 'free' straight portion in stirrups. The math is straightforward, but the field habit of quoting 'just add 2d per bend' systematically over-estimates cutting lengths by 5–8 %. The BBS / Cutting Length calculator implements IS 2502 Table VIII exactly and reports the deduction per bend so you can verify each line item.

Code references (with provenance)

  • IS 2502:1963 — Code of practice for bending and fixing of bars for concrete reinforcement. Tables VIII (bend deduction) and IX (hook allowance).
  • IS 456 Cl 26.2.2.1 — Hooks: 90°/135°/180° bends with straight portion of 4φ/12φ/4φ respectively beyond the bend.
  • IS 13920 — Ductile Detailing — seismic 135° hook with 10φ straight (≥ 75 mm) extension for stirrups in seismic zones.
  • IS 1786 — High-strength deformed bars (Fe415/500/550/600).

Stirrup cutting length — IS 2502 Table VIII

Closed stirrup (2 hooks at 135°): perimeter = 2(A+E) + 2 cover on each side. For A = 220, E = 370, cover 25 mm, 8 mm bar, two 135° hooks:

perimeter = 2(220 + 370) − 8 × 25 (cover on each side, total 4) = 2 × 590 − 200 = 1180 − 200 = 980 mm.

Hook allowance per IS 2502 Table IX for 135° hook with 12φ straight portion: 12 × 8 + 2 × 8 = 112 mm per hook, × 2 = 224 mm.

Total cut length = 980 + 224 = 1,204 mm for a rectangular stirrup, before any bend deduction.

With bend deductions (Table VIII: 2d for 45°, 2d for 90°, 3d for 135°): for 2 × 90° bends = 2 × 2 × 8 = 32 mm. Final = 1,204 − 32 = 1,172 mm for the rectangular stirrup.

Compare with the simple formula 2(A+E) + 24d = 2(220+370) + 24×8 = 1,180 + 192 = 1,372 mm — that's 17 % over.

Field notes (what trips people up)

  • Bend deduction is not hook allowance. Deduction is what gets SHORTER (the bar's curved path is shorter than the straight-line dimension). Allowance is what gets LONGER (the hook projection beyond the bend). Don't confuse them.
  • Stirrups in seismic zones (IS 13920 Cl 6.3, hoops per Cl 3.4) need 135° hooks with 10φ straight portion (≥ 75 mm), not 12φ. The calculator's seismic toggle handles this.
  • Hook at free end of a longitudinal bar adds 9φ + 9φ = 18φ (90°) or 12φ + 3φ = 15φ (135°) — different from stirrup hook.
  • Washer plates at hooks reduce the hook allowance if specified — IS 2502 Table IX notes give plate thicknesses.

Worked example

Site: 25 rectangular stirrups 220 × 370 mm, 8 mm Fe500, normal (non-seismic) zone.

Output: 1,172 mm cut length per stirrup × 25 = 29.3 m total · mass = 29.3 × 0.395 = 11.6 kg · at 1,500 ₹/quintal procurement = ₹174.

FAQ

What's the simplest shortcut for stirrups?

For 8–10 mm bars in non-seismic zones, perimeter + 24d (hook + bend) is a defensible quick estimate. For seismic zones or bars above 12 mm, calculate per bend with IS 2502 Table VIII.

Does the calculator handle crank bars?

Yes — crank (bent-up) bars are 45° bends plus straight legs. The calculator's per-bend deduction handles each 45° as 1d deduction.

Why does IS 2502 give different bend deductions for different bar diameters?

Smaller bars bend tighter (smaller bend radius). IS 2502 Table VIII accounts for this — a 6 mm bar bent 90° has a 1d deduction; a 32 mm bar has a 3d deduction.

Related reading & tools

Indicative tool — not a substitute for engineering judgement. Results are computed from formulae and reference values cited to Indian Standards and other published codes as named on this page, using nominal default assumptions; clause and table references are given in good faith for study and preliminary checks. Always verify the current edition and amendments of any cited standard in the BIS catalogue before relying on it. Final mix proportions, structural checks and construction decisions must be confirmed by a qualified engineer against the project design brief, drawings and site conditions. ConcreteInfo accepts no liability for design, procurement or construction decisions taken on the basis of these tools. Code references & rights: Indian Standards are the property of the Bureau of Indian Standards (© BIS) — official PDFs at bis.gov.in. Shared in good faith as technical reference for the civil engineering fraternity — always verify against the official publication.