Sling angle and tension calculator

Check how sling angle multiplies the tension in each leg — a screening aid for rigging, never a lift plan.

Load including rigging (kg)Number of sling legsSling angle from horizontal (°)Working load limit per leg (kg, from tag)

Tension per leg577.4 kg

Utilisation vs tag WLL: 57.7% · at 60° the factor is 1.155, at 45° it is 1.414, at 30° it is 2.000

Screening aid only — never a lift plan. The tag WLL, sling inspection, hitch type, load balance and a qualified rigger govern every lift. A calculation cannot pass a damaged or wrongly rated sling.

Formula

Tension per leg = (load / number of legs) / sin(angle from horizontal). The multiplier is 1.155 at 60°, 1.414 at 45° and 2.000 at 30°.

Standard / source

ASME B30.9 (slings) — working load limits, design factors and inspection rules. The tag WLL already includes the design factor; this calculator only compares tension against it.

Worked example

1000 kg on 2 legs at 60° from horizontal: tension per leg = (1000/2)/sin 60° = 500/0.8660 ≈ 577.4 kg. At 30° the same rig sees (1000/2)/0.5 = 1000 kg per leg — double the load share.

Safety note

SAFETY-CRITICAL — screening only, never a lift plan, never a compliance or approval verdict. Below 30° from horizontal the calculator shows a hard STOP warning: do not lift at that angle on this basis. Every lift needs a qualified rigger, inspected slings within their tag WLL, correct hitch, balanced load and the site lifting procedure.