Crane Lift Capacity and Utilization
Net capacity at the radius you enter from the OEM gross number, the hook block and rigging deduction, utilization against the site policy, and what a radius change asks for.
A 20 ton at 20 ft is 15,200 lb gross on a typical 30 ton truck crane chart. Deduct the 1,200 lb hook block and 600 lb rigging and the net is 13,400 lb, so a 12,000 lb load is at 89.6 percent utilization, over a 75 percent policy and a critical-lift trigger.
How the math works
- Net capacity: chart capacity is gross, and the hook block, the ball, the jib, the boom hoist reeving, and the rigging all count against it (ASME B30.5 and the OEM chart note). Net = gross minus hook block minus rigging, and nothing in the lift goes free.
- Utilization: load divided by net capacity. Above 75 to 80 percent is the critical-lift band on most site policies (ASCE 30-21 lift planning, OSHA 1926.1400 for cranes in construction), and above 100 percent the lift is not permitted.
- Configuration: fully extended outriggers on 360 degrees is the full chart. Limited lateral, rear-only, and over-the-tail configurations have their own charts at a fraction of the capacity, and a rough-terrain crane on rubber is a pick-and-carry machine with a 120-degree frontal pick zone and no lifting on a side slope.
- Wind: ASME B30.5 and ASCE 30 require the wind plan, and the OEM limit (commonly 20 mph on a full chart, 30 mph on a light load, and lower for high-sided picks) is the ceiling. Wind pressure scales with the square of speed, so 20 mph is 1.78 times the load of 15 mph on a sail.
- Radius: capacity falls fast with radius on a telescopic boom: chart reads are at the boom angle, and the 20 ft to 30 ft step on a mid-angle boom commonly costs 25 to 45 percent of gross. The only honest scaling is the chart.
What is net capacity on a crane?
Chart capacity minus everything hanging off the boom: the hook block, the ball, the jib, the reeving, and the slings and spreader. On a 15,200 lb gross at 20 ft, a 1,200 lb hook block and 600 lb of rigging leaves 13,400 lb of net, and a 12,000 lb load sits at 90 percent utilization.
What is the 75 percent crane rule?
A site lift policy that caps utilization at 75 to 80 percent of net chart capacity so a radius change, a wind gust, or a hook height surprise does not put you on the chart limit. It is not in ASME B30.5 as a number; it is the operator and the lift supervisor setting, and it is what most general contractors write into their crane program.
How much wind stops a crane lift?
Above 20 mph on a full chart is the working ceiling for most mobile cranes, and the OEM wind limit on the chart page is the hard number. Above 30 mph most site policies stop the lift entirely, and a high-sided load (a truss, a wall panel, duct, a sign) loses control of the lift at much lower wind than the hook load suggests.
Does crane capacity drop with radius?
Fast, and not linearly. A 30 ton crane at 20 ft reads about 15,200 lb on a common chart, and at 40 ft on the same boom configuration it reads about 6,000 lb. The chart is a function of boom angle and radius, so a radius change means a new chart read, not a percentage.