Rigging Sling Angle & Load Calculator

How it works

Leg tension = (load ÷ carrying legs) × (1 ÷ sin θ), θ from horizontal (load-angle factor: 90° 1.0, 60° 1.155, 45° 1.414, 30° 2.0); sin θ = headroom ÷ leg length, cos θ = half spread ÷ leg length; horizontal force per leg = share ÷ tan θ; 4 legs rated as 2

Two slings sharing a load do not each carry half unless they hang vertically; as the legs spread apart the tension climbs by the load-angle factor — 1.15 at 60°, 1.41 at 45° and a full 2.0 at 30°, the angle below which most standards forbid rigging because the slings are working twice as hard and squeezing the load hard sideways. A sling’s tag rating is its vertical working load limit, so the required rating is the leg tension, and riggers select the next size up after allowing for hitch type and any design factor. Four-leg bridles are rated as two legs, since a stiff load inevitably hangs on two; three legs share only when the centre of gravity sits at their centroid. An off-centre CG shifts load to the nearer leg, and the headroom the geometry demands is what decides whether the lift fits under the hook.

Worked example

An 8,000 lb load on a two-leg bridle at 45°: each leg carries 4,000 × 1.414 = 5,657 lb and pushes 4,000 lb horizontally into the load, so each sling needs a vertical rating of at least 5,657 lb — a ½″ wire-rope sling (WLL ≈ 5,600 lb) is marginal; go to 9/16″. With a 14 ft spread the legs are 9.9 ft and need 7 ft of headroom; at 30° the tension would be 8,000 lb per leg.

Frequently asked questions