TryBuildCalcSteel Bend Deduction CalculatorBend deduction and hook allowance estimator
Build a bar bending schedule with cutting length, bend/hook deductions, and total weight.
🕒 Last updated: August 11, 2026
Global Settings
ℹ️Applied at both ends of every stirrup/ring hook — commonly 9× diameter, confirm against your applicable code.
Cost
Bar Marks
This schedule needs approximately 13.9 kg (0.014 tonnes) of reinforcement steel across 1 bar mark.
| Bar Mark | Member | Shape | Dia (mm) | Bars/Member | Members | Cutting Length (m) | Total Length (m) | Unit Wt (kg/m) | Total Wt (kg) |
|---|---|---|---|---|---|---|---|---|---|
| L1 | Footing | L-Bend | 16 | 6 | 1 | 1.468 | 8.81 | 1.580 | 13.92 |
Summary by Diameter
16mm — 6 bars, 8.8 m total: 13.9 kg
Grand Total
Total Bars: 6
Total Length: 8.8 m (29 ft)
Total Weight: 13.9 kg (0.014 tonnes)
Assumptions Used
Unit weight: d² ÷ 162 (kg/m) | Bend deduction: 1d/2d/3d at 45°/90°/135° | Hook length factor: 9d
Not sure why cutting length is shorter than the outer dimensions? Bar Bending Schedule (BBS) Guide →
Bar Shape Reference
Diagram simplified for clarity (not to scale). Illustrative only.
See the complete Bar Bending Schedule Calculator guide for the full formula walkthrough, verification checklist, and FAQ.
Bend deduction and hook allowance at common angles
This page pre-fills an L-bend row: cutting length = Leg A + Leg B − bend deduction, where the deduction is 1 × diameter at 45°, 2 × diameter at 90°, or 3 × diameter at 135°, applied once per bend.
Skipping this deduction and simply adding leg lengths overestimates cutting length and wastes material at scale — it's one of the most common BBS calculation mistakes.
- Bend deduction = 1 × diameter (45°), 2 × diameter (90°), 3 × diameter (135°).
- Applied once per bend — an L-bend has one bend, a cranked bar has two.
- A rectangular stirrup applies this same 90° deduction four times, once per corner.
How Is Cutting Length Calculated?
Every bar mark follows the same overall sequence — calculate the shape's raw geometric length, subtract bend deductions, add any hook allowance, then add one lap length if a splice is included — but the raw-length formula itself differs by shape.
Step 1 — Raw Length by Shape
Straight = Length (A)
L-Bend = Leg A + Leg B
Rect. Stirrup = 2 × (Inside Width + Inside Depth) + 4 × Diameter
Circular Ring = π × Ring Diameter
Cranked = Straight A + (Rise ÷ sin(Bend Angle)) + Straight C
The rectangular stirrup and circular ring shapes are closed loops measured around their perimeter or circumference; the stirrup's inside width and depth are converted to a centerline perimeter by adding 4 × diameter (the bar sits half a diameter outward from the inside face on each of the four sides) before any bend deduction is applied. The cranked shape's inclined segment length is derived from the vertical rise and the bend angle using basic trigonometry.
Step 2 — Bend Deduction
Deduction per bend = 1 × diameter (45°), 2 × diameter (90°), 3 × diameter (135°)
L-Bend / Cranked: 1 bend (or 2 for cranked) deducted once each
Rect. Stirrup: 4 × 90° corner deductions
Steel compresses slightly on the inside of a bend, so the finished bar is shorter than the sum of its straight-line legs — this deduction corrects for that per bend in the bar.
Step 3 — Hook Allowance (Stirrups & Rings Only)
Hook Allowance = 2 × (Hook Length Factor × Diameter)
Applied once at each end of a stirrup or ring's open loop before it's closed — not applicable to straight, L-bend, or cranked shapes.
Step 4 — Lap Length (Optional)
Cutting Length = Raw Length − Bend Deduction + Hook Allowance + (Lap Multiplier × Diameter, if included)
Include a lap length only for a bar mark that splices onto another bar of the same mark to exceed one stock length.
Step 5 — Total Length and Weight
Total Bars = Bars per Member × Number of Members
Total Length = Cutting Length × Total Bars
Unit Weight (kg/m) = Diameter² ÷ 162
Total Weight (kg) = Total Length × Unit Weight
The diameter² ÷ 162 formula is the standard basis for reinforcement steel weight and is the same figure suppliers use for billing.
Worked Example (First Bar Mark)
This example walks through the first bar mark in your schedule above, using the same steps from the formula section — every other bar mark in the schedule follows the identical method.
Bar Mark Used: L1
| Input | Value |
|---|---|
| Shape | lbend |
| Diameter | 16 mm |
| Bars per Member × Members | 6 × 1 = 6 bars |
Step 1-4 — Cutting Length
| Calculation | Substitution | Result |
|---|---|---|
| Shape length (after bend/hook deductions) | Per shape formula in Step 1-3 | 1.468 m |
| Final cutting length | Shape length − deductions + hooks/laps | 1.468 m (4.82 ft) |
Step 5 — Total Length and Weight
| Calculation | Substitution | Result |
|---|---|---|
| Total length | 1.468 × 6 | 8.81 m |
| Unit weight | 16² ÷ 162 | 1.580 kg/m |
| Total weight | 8.81 × 1.580 | 13.92 kg |
Therefore, bar mark L1 needs 6 bars cut to 1.468 m each, totalling 13.92 kg.
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Disclaimer: This calculator provides approximate results for planning and estimation purposes only. Actual requirements may vary based on site conditions, materials, workmanship, and local building regulations. Always consult a qualified engineer, architect, or construction professional before making final decisions.