A crane's lifting capacity depends on how large a load its main wheel can bear. This load depends primarily on the crane's rated capacity load, but you also need to take other factors into account. Each crane comes with an impact allowance factor, which describes the relative importance of the rated capacity load. The crane's total lifting capacity is also slightly more than calculations would otherwise suggest because of added capacity from additional crane components.
Multiply the main wheel's rated load capacity by the impact allowance factor. If, for instance, the wheel offers a rated load capacity of 90 tons, and the impact allowance factor is 1.25, your equation will be 90 x 1.25 = 112.5.
Add half of the crane's weight. If the crane weighs, for instance, 3 tons: 112.5 + 1.5 = 114.
Add the combined weight of the crane's trolley and hoist. If they weigh, combined, 1.6 tons: 114 + 1.6 = 115.6.
Divide the answer by 2: 115.6/2 = 57.8. The crane's lifting capacity is 57.8 tons.