Sling Angle Calculator
This sling angle calculator works out the tension in each leg of a multi-leg sling from the load weight and the sling angle. Enter the load, the number of legs, and either the angle from horizontal or the sling length and height, and the sling angle calculator returns the tension per leg, the load angle factor, the horizontal force, and the minimum working load limit each leg needs.
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The Sling Angle Calculator is part of our Machinery collection. Browse more machinery to size, convert, and check your work alongside this tool.
What the sling angle calculator does
When a sling leg hangs at an angle, it has to pull sideways as well as up, so its tension is higher than its share of the load. The flatter the angle, the higher the tension. The sling angle calculator divides the load between the legs that carry it, applies the load angle factor 1 ÷ sin(angle), and reports the tension each leg, hook, and shackle must take.
Sling tension formula
W is the load, n the number of legs that share it, and θ the sling angle measured from horizontal. From the dimensions, sin θ = H ÷ L, where H is the vertical height from the hook to the attachment point and L the leg length. The horizontal force each leg puts on the load is the tension times cos θ.
Sling angle calculator example
A 2,000 kg machine is lifted with a two leg sling at 60 degrees from horizontal:
The load angle factor is 1.155, so each leg carries 15.5% more than half the load. Each leg pulls the load sideways with 577.4 kg. At 30 degrees the tension would be 2,000 kg per leg, double the share of a vertical lift.
How to use the sling tension calculator
Enter the load weight in any unit, kg, lb, or tonnes; the results come out in the same unit. Choose the number of legs. For a 4-leg sling on a rigid load, the safer option assumes only 2 legs carry the load, as many rigging standards advise. Then enter the sling angle from horizontal, or choose the dimensions option and enter the leg length and the vertical height from the hook to the load. Press Calculate.
Reading the sling leg tension result
The minimum WLL per leg is the tension each leg sees; choose slings, shackles, and hooks rated at least that high, or use the rated capacity of the sling assembly at that angle from the manufacturer tag. Below 45 degrees the tension rises quickly, and below 30 degrees from horizontal sling angles must not be used unless the sling maker or a qualified person approves. Uneven leg lengths or an off-center load put more weight on one leg.
When to use a rigging angle calculator
- Planning a lift with a two leg sling or bridle
- Checking a 4 leg sling on a rigid load
- Choosing sling length for the headroom you have
- Rating shackles and lifting points for the leg tension
- Reading a sling angle chart for a toolbox talk
Common sling angle mistakes
- Measuring the angle from vertical. This tool uses the angle from horizontal.
- Counting all four legs. Rigid loads often hang on two.
- Ignoring rigging weight. Add hooks, shackles, and spreaders to the load.
- Short slings. They give flat angles and high tension.
Tips for safe sling angles
- Keep sling angles at 60 degrees or more where headroom allows.
- Use a spreader beam for long or fragile loads.
- Check the sling tag for the rated capacity at the angle you use.
Two leg sling versus 4 leg sling
A two leg sling shares the load evenly as long as the lifting points are level with the center of gravity between them. A 4 leg sling looks stronger, but on a stiff load like a steel frame or a concrete panel the legs are never exactly the same length, so two diagonal legs often carry almost everything. That is why the 4 leg option here can assume only 2 carrying legs. Weigh or calculate the load first; the steel weight calculator covers plates, beams, and bars, and add the rigging weight.
Sling angle factor and the forces on the load
Each angled leg also pulls the attachment points toward each other with the horizontal force, which can bend a thin beam or tear a lifting lug sideways. Spreader beams remove that squeeze by keeping the legs vertical. Pulley and block arrangements change the force in a hoist line, which the mechanical advantage calculator covers, and a lift that starts or stops quickly adds dynamic force, which the force calculator shows from the acceleration.
Sling angle chart: load angle factor
| Angle from horizontal | Load angle factor | Tension per leg, 1,000 lb on 2 legs |
|---|---|---|
| 90° | 1.000 | 500 lb |
| 75° | 1.035 | 517.6 lb |
| 60° | 1.155 | 577.4 lb |
| 50° | 1.305 | 652.7 lb |
| 45° | 1.414 | 707.1 lb |
| 40° | 1.556 | 777.9 lb |
| 30° | 2.000 | 1,000 lb |
Sling Angle Calculator FAQ
How do you calculate sling tension?
Divide the load by the number of legs that carry it and by the sine of the sling angle: T = W ÷ (n × sin θ).
What is the best sling angle?
60 degrees or more from horizontal keeps the load angle factor at 1.155 or less. 45 degrees is a common minimum for planning.
Why not use sling angles below 30 degrees?
Below 30 degrees the leg tension exceeds the full load on a two leg sling and climbs very fast, so standards forbid it without approval.
How many legs of a 4 leg sling carry the load?
On a rigid load, usually only 2 or 3 legs take the weight, because the legs are never exactly equal. Many plans assume 2.