Specification
Working load limit and sling angle: the arithmetic that catches people out
Updated August 1, 2026 · 3 minute read · All guides
In short
Working load limit is the maximum load a sling may carry in the configuration it was rated for. For a multi-leg sling, the rating assumes a specific angle, normally a 60 degree included angle. As the angle between the legs closes, tension in each leg rises sharply: at a 30 degree included angle, each leg of a two-leg sling carries roughly 1.93 times the tension it would carry vertically. Using a sling outside the angle it was rated for is the most common way a correctly rated sling is overloaded.
Key facts
- Multi-leg sling ratings are stated at an assumed included angle, usually 60 degrees. Check the tag.
- Closing the angle increases leg tension. It does not stay proportional to the number of legs.
- Two-leg load factor: 1.000 vertical, 0.966 at 60 degrees per leg share, rising sharply below 45 degrees.
- A four-leg sling is normally rated on the assumption that only three legs take load, because loads are rarely perfectly level.
- If your crews rig tighter than the tag assumes, specify the sling against the real angle rather than the ideal one.
Why angle changes everything
When a load hangs from two sling legs, each leg carries part of the weight, but it also carries a horizontal component that grows as the legs spread. The wider the spread, the more of the leg's capacity is consumed pulling sideways instead of holding the load up.
The multiplier applied to leg tension, based on the included angle between the legs:
| Included angle | Tension multiplier per leg | Effect |
|---|---|---|
| 90 degrees (vertical, single leg) | 1.00 | Baseline |
| 60 degrees | 1.155 | The normal rating basis |
| 45 degrees | 1.414 | 41 percent more leg tension |
| 30 degrees | 1.932 | Nearly double |
| 15 degrees | 3.86 | Roughly four times |
The practical reading of that table: a sling used at a 30 degree included angle is doing almost twice the work per leg that the same sling does vertically. Slings do not fail because someone lifted something twice as heavy as the tag said. They fail because someone rigged short.
The rating on the tag assumes something
This is the part worth internalising. A multi-leg sling tag does not say "this sling can lift X". It says "this sling can lift X when rigged at the angle it was rated for". That angle is normally a 60 degree included angle, and it is stated on our product pages and on the tag.
Three consequences:
- Shorter slings on a wide load close the angle. The fix is a longer sling or a spreader bar, not a heavier one.
- A spreader bar changes the geometry, not just the capacity. Putting a bar between the pick points brings the legs back toward vertical, which is why a spreader bar often solves a problem that looks like a capacity problem.
- The same sling on a different load is a different rating. Crews who move a sling between jobs are changing the angle every time.
Why four legs are not twice two legs
A four-leg sling is normally rated on the assumption that only three legs carry load. That is not a manufacturer being conservative for the sake of it. Unless a load is perfectly rigid and perfectly level, and the four legs are exactly equal in length, the load will settle onto three legs and the fourth will go slack.
If you have ever watched a four-leg sling take up on a skid and seen one leg hanging loose, you have seen the reason for the rating basis.
Our four-leg ratings follow the manufacturer chart on that basis. Where a genuinely rigid, level load justifies a different assumption, that is an engineering question and we will refer it as one.
Choked and basket hitches
Angle is not the only geometry that changes a rating:
- Vertical hitch: the baseline. Full rated capacity.
- Choker hitch: typically reduced to around 80 percent of the vertical rating, because the chain bends sharply through the choke and the load is not evenly distributed.
- Basket hitch: up to twice the vertical rating when the legs are vertical, reducing as the legs angle in, and only where the bend radius over the load is adequate.
If a crew is choking a sling that was specified for vertical use, the effective rating dropped the moment they did it.
How to specify against reality
The single most useful thing a buyer can tell us is not the load weight. It is how the sling actually gets used:
- The heaviest load it will lift
- The typical spread between pick points, and the shortest reach available
- Whether it is choked, basketed or used vertically
- Whether the load is rigid and level, or a frame that flexes
With those, we specify the assembly against how it is rigged rather than against an ideal that never happens on site. That usually means a longer reach or a heavier grade, and it is materially cheaper than the alternative.