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: July 4, 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
Approximate results for planning only. Verify with a professional.
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.
What Is a Bar Bending Schedule (BBS) Calculator?
A Bar Bending Schedule is the site/fabrication-level document that lists every distinct reinforcement bar mark in a structure — its shape, diameter, cutting length, and total weight — used directly to cut and bend steel before it's placed. This calculator lets you build that schedule bar mark by bar mark, covering five common shapes (straight, L-bend, rectangular stirrup, circular ring, and cranked/bent-up bar), each with its own bend deduction and hook allowance, and totals the whole schedule's weight by diameter and grand total.
Add one row per bar mark using the "+ Add" buttons, fill in that mark's dimensions, diameter, and quantities, and the schedule table, weight summary, and optional cost update immediately.
What makes this calculator different:
Existing steel calculators on this site (beam, column, slab, footing steel) estimate the total reinforcement quantity for one element type. This tool instead builds the actual cutting-length deliverable — a real bar bending schedule table — from an arbitrary mix of bar marks and shapes across an entire job, which is the document a fabrication yard or site bar-bender actually works from.
Applicable standards:
- Bend deduction and hook length conventions are commonly referenced in codes such as IS 2502 (India) and BS 8666 (UK) — always confirm the exact values against your project's applicable structural code
- Bar mark shapes, dimensions, and quantities must come from the approved structural drawing, not be assumed
- This calculator estimates cutting length and weight only, not reinforcement design (bar sizing, spacing, or development length)
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.
Essential Checklist+−
Complete these critical checks before approving the work or proceeding to the next construction stage.
✓Bar Marking & Drawing Cross-Check+-
- Every bar mark in the schedule matches a bar mark shown on the approved structural drawing — no bar mark invented or omitted.
- Bar diameter, shape, and dimensions for each mark are taken directly from the drawing, not estimated or assumed.
- Steel grade (e.g. Fe415, Fe500, Fe550) recorded for each bar mark matches the drawing — mixing grades in one schedule changes both the weight and the assumed yield strength.
- The schedule is built from the latest approved drawing revision; a superseded revision number is not still in circulation at the fabrication yard.
✓Shape & Bend Deduction Verification+-
- Bend deduction values used (per 45°/90°/135° bend) match the applicable structural code or project specification, not assumed defaults.
- Hook length factor is confirmed against the drawing's hook detail (90° vs 135°) before finalizing cutting lengths.
- Deduction is applied exactly once per bend on a multi-bend shape — not doubled at a corner, and not skipped on any bend along the bar.
- Circular ring/stirrup diameter is worked out from the concrete cover reduced from the column or beam's outer dimension, not from the gross section size.
✓Lap & Splice Verification+-
- Bar marks longer than one available stock length have the correct number of lap splices accounted for, not just a single lap allowance.
- Lap length (multiple of bar diameter) matches the applicable code requirement for the bar diameter and concrete grade involved.
- Lap length used accounts for whether the splice sits in a tension or compression zone, since the two commonly require different multiples of bar diameter.
- No splice is placed inside a zone the drawing specifically prohibits (e.g. mid-span hogging zone, or a marked no-splice region near a support).
✓Cutting & Fabrication+-
- Cutting lengths are communicated to the fabrication yard or site bar-bender exactly as calculated, with no manual re-rounding that could shift bend positions.
✓Placement & Final Check+-
- Placed bar spacing, cover, and lap positions are checked against the drawing before concrete pour.
- Bar chairs and spacers are placed at the correct spacing to hold both top and bottom cover through the pour, not just at initial tying.
- Any on-site substitution of bar diameter or count (due to non-availability) is approved by the structural engineer and documented before the pour, not decided informally by the bar-bending crew.
Full QC Checklist+−
Verification checklist for bar bending schedules — covering drawing cross-check, shape/bend verification, lap splices, fabrication, and final placement. Use the Essential Checklist for critical checks; expand to Full QC Checklist for complete quality assurance.
✓Bar Marking & Drawing Cross-Check+-
- Every bar mark in the schedule matches a bar mark shown on the approved structural drawing — no bar mark invented or omitted.
- Bar diameter, shape, and dimensions for each mark are taken directly from the drawing, not estimated or assumed.
- Bar mark quantities (bars per member × number of members) match the drawing's bar spacing and member count.
- Steel grade (e.g. Fe415, Fe500, Fe550) recorded for each bar mark matches the drawing — mixing grades in one schedule changes both the weight and the assumed yield strength.
- The schedule is built from the latest approved drawing revision; a superseded revision number is not still in circulation at the fabrication yard.
- Each bar mark is labeled with its structural element (footing, column, beam, or slab) and pour/zone, so schedules for different pours aren't mixed together.
✓Shape & Bend Deduction Verification+-
- Bend deduction values used (per 45°/90°/135° bend) match the applicable structural code or project specification, not assumed defaults.
- Hook length factor is confirmed against the drawing's hook detail (90° vs 135°) before finalizing cutting lengths.
- Complex or irregular shapes not covered by the five standard shapes are calculated separately and added to the schedule manually.
- Deduction is applied exactly once per bend on a multi-bend shape — not doubled at a corner, and not skipped on any bend along the bar.
- Bar diameter used in the deduction/hook formula matches the actual diameter being cut, not a rounded or substituted diameter from a different bar mark.
- Circular ring/stirrup diameter is worked out from the concrete cover reduced from the column or beam's outer dimension, not from the gross section size.
✓Lap & Splice Verification+-
- Bar marks longer than one available stock length have the correct number of lap splices accounted for, not just a single lap allowance.
- Lap length (multiple of bar diameter) matches the applicable code requirement for the bar diameter and concrete grade involved.
- Lap locations are staggered per the structural drawing rather than all splices falling at the same cross-section.
- Lap length used accounts for whether the splice sits in a tension or compression zone, since the two commonly require different multiples of bar diameter.
- Mechanical couplers, where specified as an alternative to lapping for large-diameter bars, are used exactly where the drawing calls for them rather than substituted with an ordinary lap.
- No splice is placed inside a zone the drawing specifically prohibits (e.g. mid-span hogging zone, or a marked no-splice region near a support).
✓Cutting & Fabrication+-
- Cutting lengths are communicated to the fabrication yard or site bar-bender exactly as calculated, with no manual re-rounding that could shift bend positions.
- Bending machine or manual bending equipment is set to the correct bend angles and hook dimensions for each bar mark.
- A sample bar of each new shape is checked against the drawing dimensions before the full batch is cut.
- Bar tagging at the fabrication yard uses the same bar-mark system as the schedule, so bundles aren't mixed up in transport to site.
- Cut ends are free of burrs, cracking, or crushing that could reduce the effective cross-section at a splice or anchorage location.
- Offcut length from each stock bar is tracked and reused where the remaining piece is long enough for a smaller bar mark, rather than assumed as zero wastage in the reconciliation.
✓Placement & Final Check+-
- Fabricated bars are tagged or sorted by bar mark to avoid mix-ups on site during placement.
- Placed bar spacing, cover, and lap positions are checked against the drawing before concrete pour.
- Total fabricated weight is reconciled against the schedule's calculated total before accepting the delivery as complete.
- Bar chairs and spacers are placed at the correct spacing to hold both top and bottom cover through the pour, not just at initial tying.
- Any on-site substitution of bar diameter or count (due to non-availability) is approved by the structural engineer and documented before the pour, not decided informally by the bar-bending crew.
- Completed reinforcement is inspected and signed off by the site engineer, with a photographic record kept, before formwork is closed and concrete is poured.
Reference Tables
Bend deduction by angle
| Bend Angle | Deduction (× diameter) |
|---|---|
| 45° | 1 × d |
| 90° | 2 × d |
| 135° | 3 × d |
Standard bar diameters and unit weight
| Diameter (mm) | Unit Weight (kg/m) |
|---|---|
| 6 mm | 0.222 |
| 8 mm | 0.395 |
| 10 mm | 0.617 |
| 12 mm | 0.889 |
| 16 mm | 1.580 |
| 20 mm | 2.469 |
| 25 mm | 3.858 |
| 32 mm | 6.321 |
Typical lap length by multiplier
| Condition | Typical Lap Multiplier |
|---|---|
| Tension lap, standard grade concrete | 40-50 × diameter |
| Compression lap | 30-40 × diameter |
These are commonly referenced conventions, not a universal standard — always confirm bend deduction, hook length, and lap multiplier against your project's applicable structural code before finalizing a schedule.
Usage Guide
- Add one bar mark per distinct bar shape/size shown on the structural drawing, using the "+ Add" buttons for each shape.
- Enter dimensions exactly as shown on the drawing — inside dimensions for stirrups, leg lengths measured to the outside of the bend for L-bends.
- Only enable the lap option for bar marks that actually splice onto another bar of the same mark.
- Use the diameter summary to cross-check against your steel supplier's quote by diameter before placing an order.
- Download the checklist PDF alongside the schedule for a site-ready verification record.
Practical BBS Tips
- Keep bar marks short and consistent (A1, A2, B1...) matching the structural drawing exactly, so the fabrication yard can cross-reference without confusion.
- Measure stirrup width and depth as the inside dimension (against the inner face of the main bars), not the outside dimension of the concrete section.
- For cranked bars, confirm the rise dimension against the actual slab or beam depth minus top and bottom cover, not a generic assumption.
- Group bar marks by member on site (tag bundles) to avoid mixing up similar-looking bars with different cutting lengths.
- Always reconcile the schedule's grand total weight against delivered steel tonnage before accepting a delivery as complete.
Common Mistakes
- Adding leg lengths or perimeter without subtracting any bend deduction, overestimating cutting length and wasting material.
- Forgetting the hook allowance on stirrups and rings, leaving the fabricated loop too short to hook closed properly.
- Adding a lap allowance to every bar mark by default, even ones that fit within a single stock length and need no splice.
- Measuring stirrup dimensions to the outside of the concrete section instead of the inside face against the main bars.
- Using a fixed hook or lap convention without checking it against the project's actual applicable structural code.
Limitations
- Calculates cutting length and weight for the five shapes provided only — irregular, spiral, or multi-bend custom shapes need manual calculation.
- Does not design reinforcement (bar size, spacing, development length) — dimensions and quantities must come from an approved structural drawing.
- Assumes one lap splice per bar mark when enabled — runs needing multiple splices must be added as separate bar marks or adjusted manually.
- Visualization is an illustrative shape reference only, not a scaled drawing of your specific bars.
- Cost excludes fabrication labour, transport, and wastage/offcuts beyond the calculated cutting lengths.
Related Construction Calculators
You may also find these calculators useful for reinforcement work:
- Steel Reinforcement Calculator
Estimate overall reinforcement weight and percentage for an element.
- Beam Steel Calculator
Estimate main bar and stirrup quantities for a specific beam.
- Column Steel Calculator
Estimate longitudinal bar and tie quantities for a specific column.
- Slab Steel Calculator
Estimate main and distribution bar quantities for a slab.
- Footing Steel Calculator
Estimate reinforcement quantities for an isolated footing.
- Rebar Weight Calculator
Quick single-bar weight lookup by diameter and length.
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.