Rigging tools
Sling calculator
Start from the one thing you know — the angle you want, the slings you have, or the headroom under the hook — and get the rest: leg length, headroom, the load in every leg, and the smallest sling of each type that carries it. Off-centre loads included.
How it works
Loads are calculated. Capacities are published. The two never mix.
Every figure on this page is one or the other, and each one says which.
The geometry
Each leg is a right triangle: horizontal run, vertical rise, and the leg itself. Give it any one of angle, leg length or headroom and the other two follow. For three and four legs the run is measured across the diagonal, which is why a 4-leg on a 6 × 8 ft pattern needs the same legs as a 2-leg on a 10 ft spread.
The load in each leg
Total weight, divided by the legs sharing it, multiplied by 1 ÷ sin(angle). At 60° that is 1.15×; at 45° it is 1.41×; at 30° each leg carries as much as the whole load would on a single vertical sling. Below 30° ASME B30.9 stops you, and so does this page. With an off-centre CG the legs carry unequal loads and the page solves the statics for both.
The sling sizes
Read straight from the published charts for Sharrow web slings, polyester roundslings, Flemish-eye wire rope and Grade 80 / 100 alloy chain. Where a chart has a column for your exact hitch and angle, that column is used at the next charted angle below yours. Where it doesn’t, the load in the worst leg is checked against the published vertical rating — and the row tells you so. Nothing is interpolated, and nothing above the chart is guessed at.
Read before you rig
- The sling’s own tag is the authority. If it disagrees with this page, the tag wins.
- Protect synthetics from every edge. A corner will cut a web sling at a fraction of its rating.
- Wire rope basket ratings assume the load is at least 25 rope diameters across.
- Choker ratings assume a choke angle of 120° or more. Tighter than that, the rating drops.
- Heat, chemicals and UV all reduce capacity. Ask us about the environment if in doubt.
- Inspect before every use. A sling that fails inspection has no rating at all.
Unsure? Send us the lift.
Weights, dimensions and a photo are enough. We size and build slings every day, and we'd rather answer a question than replace a sling.