Wire Rope Load Calculator

Formula

• Empirical MBL (kN) ≈ K · d², with K from wire type × construction (optional grade multiplier).
• SWL = MBL / design factor (typical 5:1 general, 6:1 personnel, 3.5:1 static).
• Sling capacity = SWL × angle factor (single = 1; two-leg = 2·cos θ; four-leg ≈ 4·cos θ·0.866).
• Utilization = applied load / sling capacity × 100%.
• Mass per metre ≈ Cw · d² (kg/m); total mass = mass/m × length.
• Reel length L ≈ (A+D)·A·B·K_d with A = (flange−barrel)/2 − freeboard; screen 3 dead wraps and 80% recommended working.

How it works

Three modes: (1) SWL and sling capacity from empirical MBL ≈ K·d² (or catalog MBL), design factor presets, and multi-leg angle factors; (2) rope mass from length; (3) reel/drum capacity with freeboard and dead-wrap screens. Approximate only — use manufacturer certificates for release.

Pick Input mode (SWL default) or a Quick preset. The animated sketch switches with the mode: hoist elevation (single / two-leg / four-leg), cut-length mass bar, or reel section with H/D/B/X. Wire type and construction stay visible in every mode (they drive MBL and mass/m). CALCULATE fills Results. Editing a field clears Results. RESET restores 12 mm galv 6×19 · SF 5 · single leg.

SWL from diameter is the everyday path

MBL = 0.32 × 12² = 46.08 kN.

SWL = 46.08 × 1000 / 9.81 / 5 ≈ 939 kg (single vertical leg).

Mass per metre and reel fill

Mass/m ≈ 0.0036 × d² for galv 6×19 (typical screening).

Reel A = (H−D)/2 − X; L from (A+D)·A·B·K; subtract 3 dead wraps for working length.

What this pad is not

Worked example

Default SWL and sling capacity: 12 mm galvanised 6×19, design factor 5, single leg. Reproduce on CALCULATE.

1. Leave Quick preset on 12 mm galv 6×19 · SF5 · single (or enter the same values).
2. CALCULATE → MBL = 46.08 kN, SWL ≈ 939 kg, mass/m ≈ 0.518 kg/m.
3. Two-leg example: 16 mm, two-leg @ 30°, applied 1500 kg → utilization ≈ 52% (Safe).
4. Mass example: 12 mm × 100 m → total ≈ 51.8 kg.
5. Reel example: flange 500 / barrel 200 / traverse 300 / freeboard 25, Ø12 → full L ≈ 266 m.

Result: Default SWL ≈ 939 kg. Two-leg 16 mm screen stays under capacity at 1500 kg. Mass ≈ 51.8 kg / 100 m. Reel ≈ 266 m full.

When to use

• First-pass SWL from diameter, construction, and design factor
• Checking multi-leg sling capacity at a known angle
• Estimating rope mass for a cut length or reel fill
• Screening drum capacity with freeboard and dead wraps
• Comparing empirical MBL to a catalog certificate value

Limitations

• Empirical K·d² is a screen, not a manufacturer certificate. Prefer catalog MBL for release.
• Catalog MBL override ignores the empirical K and grade multiplier for strength (still applies design factor and sling geometry).
• No termination, splice, or end-fitting efficiency maps.
• No dynamic / shock load factors or bending fatigue (D/d) life.
• Not filament-SMYS or fibre-rope selection.
• Reel formula assumes uniform winding; non-uniform spooling reduces capacity.
• Always follow local lifting regulations and qualified rigger sign-off.

FAQ

What design factor should I use?

General lifting often uses 5:1 on breaking strength. Personnel or critical lifts commonly use 6:1 or higher. Static guy screens sometimes use about 3.5:1. Your code and employer rules control the choice.

Why does sling angle matter?

Legs at an angle from vertical share load through cosine components. Shallower angles raise tension in each leg and cut the hitch capacity. Many shops avoid going under 30° from vertical.

SWL or WLL?

Safe working load (SWL) is the older term; working load limit (WLL) is the modern label for the same idea: MBL divided by the design factor. This pad labels the result SWL because that is still the common search phrase.

When should I use catalog MBL?

Whenever you have a manufacturer certificate or catalog row for the exact rope. Enter that MBL in kN and the pad skips the empirical K·d² screen for strength, still applying your design factor and sling geometry.

What are dead wraps on a reel?

The first wraps that stay on the drum to anchor the rope by friction. ASME B30.7-style practice often keeps at least three. This pad subtracts three barrel circumferences from full capacity for a working-length screen.