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OBRAS ONSITE · free site calculator · rigging

Sling Angle Calculator

The flatter the sling, the harder it pulls. Load and included angle in, tension per leg out - so the sling you grab actually has the capacity for the lift.

The lift (2-leg sling)

Load weight (kg) Included angle between legs
Check before you lift: tension per leg must be under each sling's WLL for the hitch you're using; the load factor comes from the standard trigonometry (leg load = W/2 ÷ cos(θ/2)). Verify against AS 4991 / the sling's tag, your lifting register and the rigger's assessment - this calculator supports the dogger's call, it doesn't replace it. Unequal legs, edge loading and dynamic factors all add load.
Crane & lifting SWMS + VOCs in the Obras Onsite catalogue · All free tools →

This is a practical site-management tool. It is not legal, engineering or regulatory advice and does not guarantee compliance or a satisfactory inspection outcome. Requirements may vary by jurisdiction, project, contract and circumstances.

Want a person to look at it?

The tools above are free and yours to use. When you need the paperwork behind them reviewed by someone who has run sites, Obras HSE Services is a live consulting business in south-east Queensland.