Calculate the reduction factor, effective lift capacity and tension in each sling leg for multi-leg sling configurations.
Enter sling angle, leg count and WLL to calculate effective lift capacity.
Reduction factor = cos(included angle ÷ 2). Keep included angle ≤ 60° for best practice. Per AS 4991 and NZS 5433 rigging standards.
As the included angle between sling legs increases, each leg carries more tension to support the same load. At 0° (vertical), no derating applies. At 60° included angle, the tension in each leg equals the vertical load (factor 1.0). At 90°, tension is 1.41× the vertical load. Above 120°, sling tension exceeds the single-leg WLL — this is dangerous and must be avoided.
AS 4991 and most rigging codes recommend a maximum included angle of 120°, but best practice and most lift plans specify no more than 90° (60° from vertical). Above 90°, the tension in each sling leg exceeds the hook load, rapidly approaching and then exceeding WLL. A maximum of 60° included angle (30° from vertical) is ideal.
No. For a 4-leg sling on an irregular load, only 3 legs may be considered load-bearing simultaneously (one leg may be slack due to slight load imbalance). Most rigging standards rate 4-leg slings at 80–100% more than a 2-leg sling, not 200% more. The exact capacity depends on angle and load distribution.