Crane Lift Plan Calculator (Gross Load & % of Chart Capacity)

How it works

Gross load = (load + rigging + block + jib/extension deductions + hoist line) × (1 + dynamic %); % capacity = gross ÷ chart capacity; radius = boom × cos(angle) + pivot offset; critical lift > 75%

A crane's load chart gives the maximum gross load at each combination of boom length and radius, and everything hanging from the boom tip counts against it — the block, the slings and shackles, a stowed jib, even the weight of hoist rope reeved below the tip — which is why lift plans build up a gross load line by line before comparing it with the chart. Capacity falls steeply with radius (roughly with 1/radius once tipping governs), so the chart is read at the next larger radius, the boom angle is converted to radius with simple trigonometry, and a common rule keeps routine lifts under 75% of chart, above which most contractors and OSHA-referenced practice call for a written critical-lift plan. Dynamic effects from starting, stopping and wind are not in the chart and are added as an allowance.

Worked example

An 18,000 lb load with 450 lb of rigging, a 900 lb block, a 1,200 lb stowed-jib deduction and 150 lb of hoist line is a 20,700 lb gross load; against a 26,500 lb chart capacity at the working radius that is 78% — a critical lift needing a written plan. A 100 ft boom at 55° with a 4 ft pivot offset gives a radius of about 61 ft and a tip 82 ft up.

Frequently asked questions