Sling angle calculator: tension per leg
The tension in each leg of a sling from the load weight, the number of legs and the angle between the sling and the horizontal, with the load angle factor.
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Tension in each leg 2,309 lb Load angle factor 1.1551 ÷ sin(angle) Share of load per leg if vertical 2,000 lb Stop working this out by handFleetZap inspection procedures can include pass/fail, photo and signature steps, so rigging and crane checks are recorded every shift.
See FleetZap Maintenance · Try the demoThe formula
Tension per leg = (Load ÷ Legs) ÷ sin(Sling angle from horizontal)
The flatter the sling, the harder each leg pulls. With the example: a 4,000 lb load on 2 legs at 60° puts about 2,309 lb on each leg, a factor of 1.155; at 30° it would be 4,000 lb each. Every sling, hook and shackle must be rated above its share, by its tag. This is a check, not a lift plan: unequal leg lengths, an off-center load and hitches change the numbers, and lifts must follow your rigging procedures and a qualified rigger’s judgment.
Using the numberWhat to do with it
- Keep sling angles at 45° or steeper where possible; many riggers set 30° as an absolute minimum.
- Inspect slings before each use and pull any with cuts, crushing, heat damage or a missing tag.
- Record crane and rigging inspections each shift; the crane inspection checklist covers the crane side.
Guides behind this calculator
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Good to know
How do you calculate sling tension?Tension per leg = (load ÷ number of legs) ÷ sin(sling angle from horizontal). A 4,000 lb load on two legs at 60° puts about 2,309 lb on each.
What is the load angle factor?1 ÷ sin(angle). It shows how much each leg's tension grows as the sling gets flatter: 1.155 at 60°, 1.414 at 45° and 2.0 at 30°.
How many legs of a 4-leg sling carry the load?Many riggers assume only two legs carry it, because the legs are rarely exactly equal. Follow your rigging procedure.
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