Formula Used
Gross suspended load
Factored planning load
Capacity utilization
Sling tension
Ground pressure
Required mat area
Wind force
How to Use This Calculator
- Enter project, crane, load, and unit information.
- Use the governing manufacturer load-chart capacity.
- Enter the worst radius across the full path.
- Describe sling geometry and each component limit.
- Enter verified support reactions when available.
- Record wind, clearance, and power-line controls.
- Complete critical-lift and pre-lift checklists.
- Calculate, review warnings, and export the plan.
- Obtain qualified approval before starting work.
Example Data
| Input | Example | Planning purpose |
|---|---|---|
| Load weight | 20 t | Base lifted object weight |
| Accessories | 3.7 t | Block, rigging, beam, and rope |
| Dynamic factor | 1.10 | Movement allowance |
| Contingency factor | 1.05 | Planning allowance |
| Chart capacity | 35 t | Worst manufacturer configuration |
| Sling angle | 60° horizontal | Leg tension calculation |
| Effective legs | 2 | Conservative load distribution |
| Mat area | 6 m² | Ground-pressure check |
| Allowable pressure | 150 kPa | Site bearing limit |
Common Planning Mistakes
- Using the object weight instead of gross load.
- Checking only the pick radius.
- Ignoring block, rope, or beam weight.
- Using nominal crane capacity instead of chart capacity.
- Assuming equal four-leg sling loading.
- Ignoring shallow sling-angle amplification.
- Estimating ground strength without site verification.
- Using generic wind limits over manufacturer limits.
- Missing power lines or underground services.
- Starting work before approvals are complete.
Safety Limitations
This calculator supports planning and screening only. It does not certify any crane, rigging, ground, or lift arrangement.
Use current manufacturer load charts and component data. Apply local regulations, project procedures, and engineered controls.
A competent person must inspect field conditions. A qualified person must approve complex or critical lifts.
Frequently Asked Questions
What weight belongs in the capacity check?
Use the total suspended weight. Include the load, block, rigging, beams, rope, and accessories.
Which radius should I use?
Use the worst radius during the complete lift. Check intermediate positions, not only endpoints.
Can I use the crane’s nominal capacity?
No. Use the applicable manufacturer chart capacity for the exact configuration.
Why does sling tension rise at shallow angles?
Each leg carries greater horizontal force. Lower angles can rapidly increase required sling capacity.
Should four sling legs share the load equally?
Not automatically. Use conservative effective legs unless equalization is verified.
How is ground pressure estimated?
The support reaction is divided by effective bearing area. Engineering checks may still be required.
Does this calculator approve outrigger mats?
No. It estimates area only. Mat strength and load spread need verification.
How should wind limits be selected?
Use the lowest applicable manufacturer, load, company, and project limit.
What makes a lift critical?
Project rules control this decision. Common triggers include high utilization and multiple cranes.
Can this calculator replace a lift plan?
No. It helps assemble one. Qualified review and field controls remain essential.