What is the cutting length formula in a BBS?

Cutting length = sum of straight runs (measured outside-to-outside) + hook allowances − bend deductions (SP 34). Typical bend deductions: 1d for 45°, 2d for 90°, 3d for 135°. A 135° stirrup hook adds 10d (minimum 75 mm, IS 13920).

What is the unit weight of steel bars?

Unit weight in kg/m = d²/162, where d is the bar diameter in mm. So 8 mm = 0.395, 10 mm = 0.617, 12 mm = 0.888, 16 mm = 1.580, 20 mm = 2.469 kg/m.

What is the lap length as per IS 456?

Lap length (IS 456 cl. 26.2.5.1) is the greater of the development length Ld and 30d in tension (24d in compression). For Fe415 with M20 concrete, Ld ≈ 47d, so the tension lap is 47d.

How do I calculate stirrup cutting length?

For a rectangular stirrup: 2×(A+B) + 2 hook allowances − bend deductions, where A and B are the outside dimensions (member size minus twice the cover). Example: a 300×450 column, 40 mm cover, 8 mm stirrup → 2×(220+370) + 2×80 − 96 = 1244 mm.

Reinforcement · IS 2502 / SP 34

Bar Bending Schedule (BBS): formulas, cutting length and a free Excel export

A Bar Bending Schedule lists every reinforcement bar in a structure — its shape, diameter, count, cutting length and weight — so steel can be cut, bent and billed correctly. This guide gives the standard Indian-practice formulas (IS 456, IS 2502, SP 34, IS 13920) and worked examples you can check by hand.

1. Cutting length — the master formula

Cutting length = Σ straight runs (outside-to-outside) + Σ hook allowances − Σ bend deductions

Straight runs are measured outside-to-outside because that is what a detailer scales off the drawing; deductions then correct for the fact that steel bends on an arc, not a sharp corner (SP 34).

Bend angle	Deduction per bend
45°	1d
90°	2d
135°	3d

Hook	Allowance
135° stirrup hook (seismic, IS 13920 cl. 7.3.2)	10d, minimum 75 mm
180° standard U-hook (IS 2502)	9d

2. Unit weight of steel

Weight (kg/m) = d² / 162 → 8 mm = 0.395 · 10 mm = 0.617 · 12 mm = 0.888 · 16 mm = 1.580 · 20 mm = 2.469

Row weight = Nos × bars per set × length (m) × unit weight — the same arithmetic as a running-bill measurement sheet.

3. Development length and lap length (IS 456)

Ld = φ · 0.87fy / (4 · τbd) · Lap = max(Ld, 30d) tension · max(Ld, 24d) compression

For deformed bars τbd is increased 60% (cl. 26.2.1.1); in compression a further 25%. Handy values: Fe415/M20 → Ld ≈ 47d, Fe415/M25 → 40d, Fe500/M20 → 57d. A bar longer than the 12 m stock length needs a lap at each splice — count laps as their own BBS line items.

4. Worked example — stirrup cutting length

Column 300×450 mm, clear cover 40 mm, 8 mm stirrup with two 135° hooks:

A = 300−80 = 220 · B = 450−80 = 370
CL = 2×(220+370) + 2×max(10×8, 75) − [3×(2×8) + 2×(3×8)]
= 1180 + 160 − 96 = 1244 mm

5. Cranked (bent-up) bars

Extra length per crank = h(1/sinθ − 1/tanθ) → 0.27h @30° · 0.42h @45° · 0.58h @60°

6. What a professional BBS must include

A schedule an auditor will pass groups bars member-wise (the running-bill abstract format): main top/bottom bars at their true run lengths, laps as separate measured items, every extra/curtailed support bar, and each stirrup zone at its own pitch (e.g. R-1 @100 near supports, R-3 @150 mid-span, R-2 @200 elsewhere) — with each row carrying the formula that produced it, so the checker only verifies and passes.

Make your BBS free in CivilOS → member-wise abstract, checkable formulas, Excel export

Draft for checking. Site conditions, splice staggering and the structural designer's notes take precedence — a licensed structural engineer must review and sign off before steel is cut.