Sling Length for Angle Calculator
Planning a two-leg lift means picking sling legs that land at a safe angle without needing more headroom than the crane has. Give this calculator the distance between your two pick points and the sling angle you want (measured from horizontal) and it returns the exact leg length, the headroom needed under the hook, and the included angle between the legs.
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 distance between the two pick points S in metres — the horizontal span the two legs bridge.
- Enter the target sling angle from horizontal θ in degrees (steeper is better; aim for 45–60° or more).
- Read off the required leg length and the headroom you must have under the hook.
How it works
Each leg drops from the hook to a pick point S/2 across, forming a right triangle. The leg length is L = (S/2) / cos θ and the vertical headroom is H = (S/2) × tan θ. The angle enclosed between the two legs at the hook is 180° − 2θ. Angles are converted to radians internally for the trig.
Worked example
Worked example. Pick points 2 m apart with a target 60° leg angle need legs of (1)/cos 60° = 2.0 m and 1 × tan 60° = 1.732 m of headroom, with a 60° included angle between the legs.
Common mistakes
- Confusing the angle from horizontal with the included angle between the legs — a 60° leg angle gives a 60° included angle, but a 45° leg angle gives a 90° included angle.
- Choosing a flat angle (small θ) to save headroom — leg tension climbs steeply as the angle flattens, overloading the slings.
- Forgetting that the hook must clear the load by the full headroom H plus the load's own height and any spreader.
Frequently asked questions
Why keep the angle above 45°?
Leg tension grows as 1/sin θ, so at 30° each leg carries far more than at 60°. Angles below about 45° from horizontal sharply raise the load in each leg and its fittings — most rigging charts stop at 45°.
Does this account for the load sharing between legs?
No — it is purely the geometry (length, headroom, included angle). To find how much force each leg actually carries at that angle, use a sling angle load factor or two-leg load share calculator.
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- Two-Leg Sling Load Share Calculator
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- Crane Lift Utilisation Calculator
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Tip: Enter any known values to calculate the remaining results.
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