Two-Leg Sling Load Share Calculator
Split a lift between the two legs of a sling and see the tension in each. For a balanced load both legs share equally; for an off-centre centre of gravity, enter the distance from the CG to each pick point and the tool weights the shares accordingly, then converts them to leg tension using the sling angle.
Enter Values
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
- Enter the total load W in kilograms and the sling angle θ measured from the horizontal.
- For a balanced load, leave the off-centre distances blank — each leg takes W/2.
- For an off-centre load, enter both a (CG to leg 1) and b (CG to leg 2) in metres; the leg nearer the CG will show the higher share and tension.
How it works
Symmetric case: each leg's vertical share is W/2. Off-centre case: shares split by the lever arms, leg 1 = W·b/(a+b) and leg 2 = W·a/(a+b), so the pick point closer to the centre of gravity carries the larger share. In both cases the tension along a sloping leg is its vertical share divided by sin(θ), where θ is the angle from horizontal, and the load factor 1/sin(θ) is the same for both legs.
Worked example
Worked example. A 2000 kg load on a two-leg sling at 60°: symmetric, each leg's share is 1000 kg and its tension is 1000/sin(60°) = 1154.7 kg. Shift the CG so a = 1 m and b = 3 m and leg 1 now takes 2000×3/4 = 1500 kg while leg 2 takes 2000×1/4 = 500 kg.
Common mistakes
- Mixing up a and b: a is the distance from the centre of gravity to leg 1 and b to leg 2, and the leg CLOSER to the CG (smaller distance) carries MORE, so leg 1's share uses b.
- Entering only one of a or b — the tool needs both distances to split an off-centre load, or neither for a balanced lift.
- Forgetting the angle effect: even a perfectly balanced load puts more than W/2 into each leg once the legs lean, because the tension is the share divided by sin(θ).
Frequently asked questions
Which leg carries more when the load is off-centre?
The leg closer to the centre of gravity. If a (to leg 1) is smaller than b (to leg 2), the CG sits nearer leg 1, so leg 1 takes the bigger share — W·b/(a+b). This is why an unevenly loaded skip or motor can overload one leg even when the total mass is well within the sling set's rating.
Does this replace a rigging study for a heavy or awkward lift?
No. It is a planning estimate that assumes the centre of gravity sits between the pick points and the load hangs steadily. The sling tag WLL/SWL, the real load mass and CG, and a licensed rigger/dogger working to AS 1418, AS 2550 and AS 4991 govern the job, and you must never lift over people.
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