What's the minimum recommended sling angle?

Per ASME B30.9-2021, the minimum recommended angle is 30° from horizontal (equivalent to an included angle β = 120° at the apex). Below this, leg tension exceeds twice the load weight and slings should be inspected for damage after every lift.

Why does a shallow sling angle dramatically increase tension?

Tension per leg follows T = W·HF / (N·sin α). As α drops, sin α drops; at 30° sin α = 0.5 so tension doubles. At 15° it triples. Always quote the angle you'll actually achieve, not the maximum the rigging permits.

What's the difference between horizontal angle α and included angle β?

α is the angle between each sling leg and the load surface (a1°/a2° in standard diagrams). β is the angle between the two legs at the hook (b1+b2). For a symmetric 2-leg bridle, α = 90° − β/2. The calculator accepts either.

Why does the centre of gravity matter for lifting?

A lift point above the CoG keeps the load stable; below it the load tips. Multi-point lifts must be planned so the resultant hook position is directly above the calculated CoG to prevent rotation in the air.

How precise do the component masses and offsets need to be?

For most rigging plans, ±5% is sufficient — the CoG shifts proportionally. Use as-built drawings where available; manufacturer mass certs trump catalogue values.

What if my load has movable components (e.g. a half-full tank)?

Calculate the CoG at the worst-case fill condition or pin moving parts before lifting. Free-surface effects in partially-filled vessels cause the CoG to migrate during the lift.

Can this tool replace the manufacturer's load chart?

No. The tool gives a simplified estimate based on radius, boom length and derating factors. The actual lift must always be cross-checked against the printed load chart for that specific crane, configuration, and outrigger setup.

Why does on-rubber lifting derate the capacity so much?

Rubber tyres flex under load, shifting the CoG and reducing stability. Most mobile cranes derate to ~75% of outrigger-mounted capacity, and many prohibit lifting on rubber entirely above certain radii.

What is the side-stability factor?

Lifts over the side or rear of the crane have less counterweight backup than over-the-rear lifts. Many load charts list separate columns for over-front, over-side, and over-rear — the tool applies a conservative derating where this matters.

What is a Mode Factor?

LEEA defines Mode Factor (M) as a multiplier on the rated single-leg WLL that accounts for the way a sling is rigged (vertical, choke, basket, parallel) and the leg angle. Effective WLL = WLL_single × M.

Why does LEEA cap β at 120°?

Beyond β = 120° (α < 30°), leg tension grows so rapidly that the small dimensional changes in the rigging cause large changes in load distribution. LEEA classifies such lifts as non-routine, requiring written justification.

How does choker hitch reduce WLL?

A choker hitch crushes the sling at the choke point, introducing bending. LEEA applies a Mode Factor of 0.8 for choker on round/wire-rope slings, 0.75 for chain — and the tool implements this lookup automatically.

What makes a lift 'critical'?

Lifts are typically classed as critical when the load exceeds 75% of crane capacity, the load is over personnel or live equipment, or the load value/uniqueness exceeds organisational thresholds. Critical lifts require a written lift plan, engineering review, and toolbox talk.

What's the difference between routine, engineered, and critical?

Routine — within standard procedures, off-the-shelf rigging. Engineered — bespoke design (custom spreader, multi-crane lift). Critical — high consequence of failure. Many organisations sit engineered and critical together.

Why does proximity to personnel raise the category?

Per OSHA 1926.1431 and most company HSE plans, lifts that suspend load over occupied spaces require additional control — secondary backup rigging, larger exclusion zones, and pre-lift sign-off.

D is the diameter the sling is bent around (pin, hook, shackle bow). d is the sling rope/chain diameter. D/d determines how much the sling's effective strength is reduced by the bend — at D/d = 1 (sling wrapped on itself) efficiency drops to 50%.

What's the LEEA minimum D/d?

LEEA recommends D/d ≥ 18 for wire-rope slings around pins and shackles (≈ 89% efficiency). For synthetic slings the minimum varies by manufacturer but is typically D/d ≥ 5–7 around hardware.

Does D/d matter for choker hitches?

Yes — the choke point is the worst case because the sling bends around itself at very low D/d. The Mode Factor for choker hitch already partly accounts for this, but tight choke points (small load diameter) require further derating.

Lifting & Rigging Calculators – Sling Load

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1Sling Load Calculator

Tension per leg: T = (W × HitchFactor) / (N × sin α) — where α is the angle between the sling leg and the load surface (the outer angle at the rigging points, marked a1°/a2° on standard diagrams). You can also enter the included angle β between the two legs at the apex (b1+b2) — the calculator converts between the two for symmetric 2-leg bridles using α = 90° − β/2. Compare against the sling Working Load Limit (WLL) to confirm safety.

Total load weight i

Number of sling legs Per ASME B30.9-2021 3 & 4-leg bridles are conservatively designed assuming only 2 legs carry the full load.

Angle measurement i

Sling angle from horizontal α (°) i

15°60°90°

Smaller angles dramatically increase leg tension. 60° (α) ≈ 60° included is the recommended minimum.

Hitch type i

Sling Working Load Limit (WLL) per leg, optional i

Result

— per leg

—

Vertical share / leg—

Load Angle Factor (LAF)—

Hitch factor—

Equivalent angle—

Total load (kg)—

vs WLL—

2Centre of Gravity Estimator

Add components (pipes, plates, vessels, motors) and the tool computes the combined CoG via mass-weighted averages: X̄ = Σ(mᵢ·xᵢ) / Σmᵢ. Use this to position lift points and prevent tipping during multi-point lifts.

Item	Mass (kg)	X (m)	Y (m)	Z (m)

Combined Centre of Gravity

Total mass— kg

CoG X— m

CoG Y— m

CoG Z— m

18Crane Load Chart Estimator

Estimate working load by operating radius and boom angle, applying the standard derating factors (configuration, on-rubber/outriggers, side-stability). Always cross-check against the actual manufacturer load chart for your crane and configuration.

Crane size class i

Boom length (m)

10 m30 m80 m

Operating radius (m) i

3 m10 m60 m

Setup

Outriggers fully extended Outriggers partial On rubber / pick-and-carry

Quadrant

Over rear Over side Over front

Planned load (kg) i

Allowable load & utilisation

— kg permitted

—

Boom angle—

Configuration factor—

Geometry factor (radius)—

Utilisation—

Tipping check (R/L)—

—

26Sling Mode Factor (LEEA)

Formal LEEA Mode Factor lookup. Effective WLL = WLL_single × Mode Factor. The Mode Factor (M) accounts for how the sling carries the load (single, choke, basket, parallel) and the leg angle. Aligned to LEEA COPSURE 1.6 / EN 13414-1:2003+A2:2008.

Sling type

Chain Wire rope Round / web

Mode i

Angle from vertical β (°) i

0°30°75°

LEEA caps included leg angles at 120° (β = 60°) — beyond this is non-routine.

Single-leg WLL (vertical, kg)

LEEA Mode Factor & effective WLL

— kg effective WLL

—

Mode Factor M—

Angle factor—

Per-leg tension @ rated load—

Reference—

—

27Lift Plan Categorisation (Routine / Non-routine / Critical)

Score-based classifier aligned to LEEA Lift Planning guidance and IOGP 376. Returns the lift category (1 / 2 / 3) with the documentation and sign-off level required.

Load weight (t)

Crane chart capacity at planned config (t)

Lift mode

Personnel exposure

Visibility

Environment

Load value / criticality

Lift category

—

Capacity utilisation—

Risk score (0–20)—

Documentation required—

Approval level—

Pre-lift requirements—

—

28D/d Ratio Calculator

Compares bend radius (D) of a sheave, drum or fitting to rope diameter (d). When D/d falls below LEEA-recommended ratios, rope efficiency drops and the WLL must be derated. References LEEA COPSURE 1.4 / 4.6 and ISO 4308.

Application

D — drum / sheave / pin / edge diameter (mm)

d — wire-rope / chain / sling diameter (mm)

Single-leg WLL (kg, optional)

Bending efficiency & derated WLL

— D/d ratio

—

Bending efficiency η—

Derated WLL—

Recommended minimum D/d—

Reference—

—

For training purposes only. Always verify with qualified personnel, the lift plan, and current ASME B30 / OSHA / LEEA / manufacturer load chart values.

39Wind Load on Lifts (Beaufort scale)

Crane lifts must be stopped or derated when wind speed exceeds the manufacturer's threshold. Tool returns drag force on the load and a derate recommendation per ASME B30.5 / EN 13000 typical practice (max 7 m/s ≈ Beaufort 4 for routine lifts; stop at 9.8 m/s / Bf 5 for blind / tandem; stop ALL above 13 m/s / Bf 6).

Wind speed (m/s)

Load projected area (m²)

Drag coefficient C_d

Lift complexity

Result

— N drag on load

—

Beaufort scale—

Dynamic pressure q— Pa

Drag force F = q·A·C_d—

Recommendation—

Reference: ASME B30.5-2021, EN 13000:2010+A1:2014. Always defer to the crane's manufacturer wind chart.

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Lifting & Rigging Calculators

1Sling Load Calculator

Result

2Centre of Gravity Estimator

Combined Centre of Gravity

18Crane Load Chart Estimator

Allowable load & utilisation

26Sling Mode Factor (LEEA)

LEEA Mode Factor & effective WLL

27Lift Plan Categorisation (Routine / Non-routine / Critical)

Lift category

28D/d Ratio Calculator

Bending efficiency & derated WLL

39Wind Load on Lifts (Beaufort scale)

Result

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