Why radius matters most
A mobile crane’s rated capacity drops quickly as the load moves away from the crane. The same crane that lifts tens of thousands of pounds close in may manage only a few thousand at full reach. That is why the distance from the parking spot to the set-down point often decides the crane class.
How this calculator works
- Adds 10% of the load (minimum 500 lb) for hook block, slings and spreader bars.
- Allows 15 ft above the set-down level for the load, rigging and hook when working out boom length.
- Picks the smallest class that keeps the lift under 75% of its estimated capacity at that radius. Many lift-plan policies treat lifts over 75% of rated capacity as critical lifts.
- Capacity at radius uses a simplified curve for each class, not a manufacturer’s chart.
Use it to ask the right question, not to plan the lift. Every crane has its own load chart, configuration and ground requirements. The operator or a qualified lift planner decides.
Crane classes used
| Class | Max radius in this guide | Max boom |
|---|---|---|
| Boom truck, up to about 30 ton | 90 ft | 110 ft |
| 40–60 ton truck or rough-terrain crane | 115 ft | 140 ft |
| 75–100 ton all-terrain crane | 150 ft | 190 ft |
| 150–250 ton all-terrain crane | 200 ft | 260 ft |