How to Calculate Sling Capacity by Angle and Leg Count
The flatter a leg pulls, the less it may carry. This guide explains the angle factor, the role of leg count and how to correctly calculate the permissible working load of a chain sling or lifting sling.
View lifting slingsWhy does the working load drop as the angle grows?
As soon as a sling leg pulls at an angle rather than straight down, the load splits into a vertical load-bearing component and a horizontal side-pull. The flatter the leg stands, the higher the tension in each leg for the same load, so the rated capacity must be reduced by an angle factor.
The angle β is measured between the leg and the vertical. At 0° the leg hangs straight and carries fully, at 45° the leg tension already rises noticeably, and at 60° it has doubled. Angles greater than 60° are not permitted, because the leg tension climbs beyond control.
Which angle factors apply?
The permissible load is the rated capacity of a single leg multiplied by the angle factor and the leg factor. The values below are set out in EN 818‑6 for chain slings and in the corresponding rigging rules.
For a symmetric two-leg sling the rated capacity of a single leg is multiplied by 1.4 (up to 45°) or by 1.0 (up to 60°). These mode factors already include the angle effect, so you can read them straight from the sling tag or capacity chart.
- Angle up to 45°: a two-leg sling carries 1.4 times a single leg.
- Angle 45° to 60°: a two-leg sling carries only 1.0 times a single leg.
- Above 60°: lifting is forbidden, leg tension too high.
- Always calculate with the largest angle that can occur.
How does the number of legs affect capacity?
A four-leg sling does not carry twice as much as a two-leg sling. Because a load is rarely shared perfectly, only two legs are counted as load-bearing on three- and four-leg slings. The leg factor therefore stays at 1.4 (up to 45°) or 1.0 (up to 60°).
- Permissible load = single-leg rated capacity x leg factor.
- With an off-centre load, base the calculation on the worst leg.
- Shortening hooks and choke hitches reduce capacity further.
- The maker's tag and capacity chart always take priority.
Frequently asked questions
What is the angle factor?
It reduces the permissible working load when a leg pulls at an angle instead of vertically. Up to 45° it is 1.0, between 45° and 60° it falls to 0.5, and above 60° lifting is not permitted.
Why do only two legs count on a four-leg sling?
Because a rigid sling never shares the load perfectly across all four legs. For safety only two legs are treated as load-bearing, so the leg factor stays at 2.1 up to 45°.
How do I calculate the permissible load?
Permissible load equals the rated capacity of one leg multiplied by the leg factor. For the angle, always assume the largest angle that can actually occur in the lift.
Which standard governs sling capacity?
EN 818 covers round-steel chain slings and EN 1492 covers webbing slings and roundslings, supported by national rigging rules for safe lifting of loads.
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