Crane Lift Capacity & Derating Calculator
Calculate crane safe working load at a specific operating radius and boom angle, applying standard derating and an 85% safety factor.
Results
What is it?
Crane capacity decreases significantly as the operating radius (horizontal distance from crane centre to load) increases. Boom angle also affects capacity � a more vertical boom is stronger. The 85% safety factor (0.85) accounts for dynamic loads, ground conditions, and rigging weight.
How to use
Enter the crane's rated capacity at minimum radius (from the load chart), the actual operating radius and minimum rated radius, and the boom angle in degrees. The calculator applies a physics-based derating formula plus the 85% working load factor to give the safe lift capacity for that lift configuration.
Example scenario
A 50-tonne crane at 5m minimum radius, operating at 20m radius with a 70� boom angle: Derating factor � 0.182. Safe working load = 50 � 0.182 � 0.85 � 7.75 tonnes. Always verify against the manufacturer's actual load chart, which is the legal document.
Pro tip
?? This calculator provides an engineering estimate only. ALWAYS use the manufacturer's certified load chart for actual lift planning � it is the legal document. Factors not modelled here include wind, ground bearing capacity, outrigger configuration, and multi-crane lifts. A certified rigger must sign off all critical lifts.