Plan lifts with sling-angle tension, hitch factors, and dynamic allowances built-in checks. Validate shackle, hook, and sling ratings before crews commit to rigging today.
Typical planning values for a two-leg lift at 60°.
| Load | Legs | Angle | Dynamic | Planning | Leg tension | Required WLL |
|---|---|---|---|---|---|---|
| 5000 kg | 2 | 60° | 10% | 1.10× | ≈ 34.3 kN | ≥ 34.3 kN per leg |
| 8000 kg | 4 | 45° | 15% | 1.15× | ≈ 31.3 kN | ≥ 31.3 kN per leg |
Rigging failures are rarely caused by one weak part; they are usually the result of underestimated tension, poor angles, and uncontrolled dynamics. This calculator converts load to kN, applies allowance multipliers, and estimates per-leg tension so crews can compare it against rated working limits.
The entered load is converted to kN and then increased using a dynamic allowance and a planning factor. For example, a 5,000 kg load is about 49.0 kN. With 10% dynamic and a 1.10 planning factor, design load becomes about 59.3 kN.
Angle is measured from horizontal. The angle factor is 1/sin(θ). At 60° the factor is 1.155, at 45° it is 1.414, and at 30° it is 2.000. Small angle reductions can double tension even when the load is unchanged.
For symmetric bridles the calculator assumes equal sharing across legs. Two-leg rigs often see higher sensitivity to geometry, while four-leg rigs can still overload one leg if the center of gravity is offset. Good practice includes equal sling lengths, matched hardware, and verified pick points.
Hitch type affects how a sling develops capacity. Planning multipliers here are common rules-of-thumb: vertical 1.00×, choker 0.80×, basket 2.00×. Always confirm the exact rated chart for the sling type, diameter, and configuration you are using.
Shackles, hooks, master links, and lifting points must each exceed the calculated leg tension. If any component utilization exceeds 100%, the system is not acceptable. Replace the limiting component, increase sling angle, reduce dynamics, or redesign the lift path and controls.
Dynamics come from hoist acceleration, wind, snagging, and sudden stops. Many lift plans use 5–15% for well-controlled crane lifts and higher allowances when conditions are uncertain. Tag lines, slow starts, exclusion zones, and clear signaling reduce dynamic amplification.
Use the CSV and PDF outputs to capture inputs, assumptions, and utilization results for review. Record sling angle, leg count, WLLs, and selected allowances. A clear record supports toolbox talks, inspections, and pre-lift authorization on active construction projects.
Enter the sling angle measured from the horizontal plane. If you measure from vertical, convert it by using θ = 90° − measured. Lower angles increase tension quickly.
No. Enter the gross lifted load you want to evaluate. If rigging weight is significant, add it to the load input or apply a higher planning factor, consistent with your lift plan.
If the load center of gravity is not centered or sling lengths differ, one leg can carry more than half the load. This calculator assumes equal sharing, so confirm balance and pick point symmetry.
Use a value aligned with site controls and conditions. Controlled crane picks may use 5–15%. Higher values may be needed for wind, difficult starts, or uncertain handling. Follow your procedures and engineer guidance.
No. Multipliers vary by sling material, construction, diameter, and manufacturer. The included values are planning defaults. Always verify the specific sling tag and manufacturer chart for final selection.
Stop and redesign. Increase component ratings, improve sling angle, add legs where appropriate, reduce dynamic effects, or reduce the lifted load. The limiting component governs the entire rigging system capacity.
No. It supports preliminary planning and documentation. Critical lifts, unusual geometry, or high-risk environments require competent person review and, when required, engineered lift plans and approved rigging arrangements.
Measure, verify, document, and lift with disciplined control always.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.