Calculate load utilisation and safety margin from the crane's rated capacity at the working radius and the actual load to be lifted.
From crane load chart at actual radius
Enter rated capacity from the load chart and load details.
Best practice: keep utilisation ≤ 80% rated capacity. Always use the crane load chart for the specific radius and configuration. Per AS 2550 / NZS 5433.
SWL (Safe Working Load) or WLL (Working Load Limit) is the maximum load a crane is rated to lift at a given boom configuration and working radius. It is read from the crane's load chart for the specific boom length, radius, and any attachments in use. SWL includes the load plus all rigging and hook block weight.
The 80% utilisation rule provides a safety buffer for dynamic loads (wind, acceleration), load weight uncertainty, and structural variability. Working at 100% of rated capacity leaves no margin for unexpected conditions. Many site-specific lift plans require staying at or below 80% for all but certified critical lifts.
AS 2550 series covers the safe use of cranes in NZ and Australia. AS 2550.1 covers general requirements, while specific parts cover mobile cranes (2550.5), tower cranes (2550.3) and overhead travelling cranes (2550.1). WorkSafe NZ Health and Safety at Work Act 2015 also governs high-risk plant including cranes.