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Sling Angle Load Factor Calculator

Work out how much extra tension a sling angle puts into each leg of a lift. Because a leaning leg carries more than its vertical share, the tension climbs as the angle from horizontal drops — this tool returns the load factor (1/sinθ), the tension per leg and, if you enter a leg's rated WLL, whether it still passes at that angle.

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How to use this calculator

Enter Values

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Enter the total load W in kilograms and the sling angle θ measured from the HORIZONTAL (90° = vertical straight lift, 60° and 45° are common two-leg angles).
  2. Set the number of legs sharing the load (default 2); optionally enter the rated WLL stamped on one leg to get a pass/fail check.
  3. Read the load factor and the leg tension — if you supplied a WLL, confirm the check says PASS before the lift and re-plan if it says FAIL.

How it works

The angle θ is measured from the horizontal. Each leg's vertical share is W divided by the number of legs n, but the actual pull along the sloping leg is that share divided by sin(θ), so leg tension = (W/n)/sin(θ) and the load factor = 1/sin(θ). The factor is 1.0 at 90°, 1.155 at 60°, 1.414 at 45° and 2.0 at 30°, then rises sharply below that. A leg's effective capacity is reduced the same way, to rated WLL × sin(θ), which the tool compares against the calculated tension.

Worked example

Worked example. A 1000 kg load on a 2-leg sling at 60° from horizontal: vertical share = 1000/2 = 500 kg, load factor = 1/sin(60°) = 1.1547, so each leg carries 500 × 1.1547 = 577.35 kg. Drop the angle to 30° and the factor doubles to 2.0, driving each leg to 1000 kg for the very same load.

Common mistakes

  • Measuring the angle from the vertical instead of the horizontal — swap the two and the whole result is wrong; this tool uses the angle up from horizontal.
  • Rigging at a shallow angle: below about 30° the tension rockets and can quietly overload a leg even though the load looks modest — keep angles as steep as practical (many sites set a 45° minimum).
  • Assuming the sling's flat vertical WLL still applies at an angle — the effective capacity drops to WLL × sin(θ), so a lower-angle lift needs a bigger sling or more legs.

Frequently asked questions

Is the angle measured from the ground or from the vertical?

From the horizontal (the ground/plane of the load). A vertical, straight-up lift is 90°; a leg leaning out to 45° is halfway. Some charts quote the included angle between two legs instead — that is a different number, so make sure you are using the angle from horizontal here.

What is the smallest angle I should rig at?

As steep as you can. At 30° the leg tension is already double the vertical share, and it climbs fast below that, so most safe-working procedures set a minimum of 30° and prefer 45° or more. This is a planning estimate only — the sling tag WLL/SWL and a licensed rigger/dogger to AS 1418, AS 2550 and AS 4991 have the final say, and you must never lift over people.

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