Example data table
| Units | Load | Rigging | Radius | Chart rated | Dynamic | Reserve | Utilization | Status |
|---|---|---|---|---|---|---|---|---|
| Metric | 6,500 kg | 450 kg | 14.0 m | 9,500 kg | 1.15 | 10% | ~92% | Within limits |
| Metric | 11,000 kg | 700 kg | 18.0 m | 12,500 kg | 1.25 | 10% | ~123% | Over limits |
| Imperial | 18,000 lb | 1,000 lb | 45 ft | 28,000 lb | 1.10 | 15% | ~86% | Within limits |
Formula used
- Gross Load = Load + Rigging + Accessories
- Required Load = Gross Load × Dynamic × Duty × Wind
- Effective Rated = Chart Rated × (1 − Reserve) × Level × Carry
- Utilization (%) = Required Load ÷ Effective Rated × 100
- Moment = Load × Radius
- Radius (optional) ≈ Boom Length × cos(Boom Angle)
How to use this calculator
- Choose units matching your crane chart.
- Enter the payload, rigging, and any accessories.
- Measure the planned lift radius at the pick point.
- Enter the chart rated capacity for your configuration.
- Set factors for dynamic effects, duty, wind, and margins.
- Submit to see utilization and moment checks above.
- Export CSV or PDF for planning and review.
Load Chart Inputs That Drive Capacity
Crane capacity is governed by the manufacturer’s load chart, which relates rated load to working radius and boom configuration. This calculator organizes the key inputs—gross load, boom length, boom angle, and radius—so you can estimate a conservative net capacity. Always compare results against the exact chart for the crane model and reeving.
Radius, Boom Length, and Angle Effects
Working radius is the horizontal distance from the crane’s center of rotation to the load’s vertical line. As radius increases, capacity typically drops sharply because overturning moment rises. Small radius errors matter: a 10% radius increase can create a similar increase in moment. Boom angle influences radius; a lower angle usually increases radius and reduces allowable load.
Rigging, Hook Block, and Attachments Allowance
Capacity charts are based on a defined “hook load,” but the total lifted weight includes more than the object. Deduct rigging weight such as slings, shackles, spreader bars, lifting beams, and the hook block. A simple field check is to list every component and its certified weight, then add contingency for water, mud, or trapped material that can add unexpected kilograms. Include dynamic allowance for starting, stopping, and snatching; 5–10% is commonly budgeted in lift plans.
Site Setup Factors That Change Real Capacity
Real capacity depends on setup. Outriggers should be fully extended and level within the manufacturer tolerance; even a small out-of-level condition shifts load and reduces stability. Ground bearing pressure must be checked using outrigger reaction forces and pad area. Wind adds side load and can require derating; track gusts and suspend lifts when conditions exceed site limits.
Planning Checks That Reduce Lift Risk
Use the calculator during lift planning to validate that the planned configuration has sufficient margin after deductions. Confirm swing clearance, pick-and-carry restrictions, and crane travel paths. Document the lift: load weight basis, chart reference, rigging plan, and communication signals. For critical lifts, add an independent peer review and a test lift near the ground.
FAQs
Is this calculator a substitute for the crane’s load chart?
No. Use it to organize inputs and estimate net capacity, then verify every lift against the exact manufacturer load chart for your crane, configuration, reeving, and setup conditions.
What should I enter as “Chart Rated Capacity”?
Enter the rated capacity from the correct load‑chart row for your boom length, counterweight, outrigger state, and planned radius. If the chart lists multiple limits, use the most restrictive value.
How do I include rigging and the hook block?
Add the hook block, slings, shackles, spreaders, and any below‑hook devices to the rigging/accessories fields. The calculator subtracts these from rated capacity to show the remaining allowance for the payload.
Why does a small radius change matter so much?
Overturning moment equals load times radius. Increasing radius increases moment directly, so allowable chart load drops quickly. Measure radius at the pick point, not from drawings alone, and recheck after repositioning.
What dynamic factor should I use?
Use your site or lift‑plan requirement first. For smooth lifts, crews often budget a modest allowance to cover starting, stopping, and minor swing. For impact, snatch loads, or poor control, increase the factor and reassess.
Can I use this for critical or personnel‑related lifts?
You can use it for planning, but critical lifts require a formal engineered lift plan and approvals. Never rely on a generic calculator for lifts over people; follow regulations, manufacturer guidance, and a qualified lift director.