Calculator Inputs
Formula Used
Adjusted Load = Base Load × Dynamic Factor × COG Factor × Planning Factor
Angle Factor = 1 ÷ sin(θ)
Here, θ is the sling angle measured from the horizontal.
Effective Support Parts = Sling Legs × Hitch Support Parts × (Load Share Efficiency ÷ 100)
Basket hitch uses 2 support parts per sling. Vertical and choker use 1.
Per Part Tension = Adjusted Load ÷ (Effective Support Parts × sin(θ))
Required Rated Capacity = Per Part Tension ÷ Choker Capacity Factor
Choker Capacity Factor = 0.80 for choker, and 1.00 otherwise.
These equations are practical planning equations for symmetric rigging layouts. They do not replace engineered lift plans for complex geometry, shock loading, side loading, unequal leg lengths, bending over edges, or nonstandard hardware arrangements.
How to Use This Calculator
- Enter the load weight and choose the matching unit.
- Select the hitch type used for the lift.
- Enter the number of sling legs involved.
- Set the share efficiency to reflect how evenly the load is shared.
- Enter the sling angle from horizontal.
- Add dynamic, center of gravity, and planning factors for your lift conditions.
- Optionally enter rated capacity per active leg or part and top hardware WLL.
- Press calculate to view results, graph, and export options.
Example Data Table
| Case | Load | Hitch | Legs | Angle | Factors | Per Part Tension | Required Rated Capacity |
|---|---|---|---|---|---|---|---|
| Pipe bundle | 2,500 kg | Vertical | 2 | 60° | 1.10 × 1.00 × 1.05 | 1,667 kg | 1,667 kg |
| Precast panel | 4.0 metric ton | Choker | 2 | 45° | 1.15 × 1.10 × 1.10 | 3.922 metric ton | 4.903 metric ton |
| Steel frame | 18 kN | Basket | 2 | 60° | 1.05 × 1.00 × 1.05 | 5.457 kN | 5.457 kN |
These examples are illustrative. Actual rigging selection must use verified equipment tags, manufacturer data, and competent lift review.
Frequently Asked Questions
1) Why does tension increase when the sling angle gets smaller?
A smaller angle reduces the vertical lifting component of each sling. To hold the same load, each active part must develop more tension. That is why low angles can overload slings quickly.
2) What is load share efficiency?
It estimates how evenly the sling legs share the lift. Perfectly equal sharing is rare. Lower efficiency gives a more conservative result because fewer effective support parts are assumed to carry the load.
3) When should I use a dynamic factor above 1.00?
Use it when motion, crane acceleration, stopping, impact, wind, or handling conditions can increase force above the static lifted weight. Higher movement uncertainty generally needs a higher planning allowance.
4) What does the center of gravity factor represent?
It accounts for uneven loading caused by off-center gravity, unequal pick points, or imperfect balance. A value above 1.00 increases the planning load to reflect that one side may take more force.
5) Why does choker mode increase the required rating?
Choker arrangements commonly reduce usable capacity because the sling bends around the load and tightens under load. This calculator uses a planning reduction factor so the required rating becomes more conservative.
6) Can I use this page for engineered critical lifts?
Use it for planning review only. Critical lifts, unusual geometry, side pulls, nonuniform slings, edge effects, shock loading, and specialized hardware need formal engineering review and approved lift documentation.
7) What should I enter for rated capacity per active leg or part?
Enter the applicable rating for the specific active leg or supporting part used in the chosen setup. Use the value that matches your manufacturer tag, hitch arrangement, and site procedure.
8) Why check top hardware WLL separately?
The hook, shackle, master link, or spreader connection may see the full adjusted load even when tension is divided among slings. A lift can fail overall if top hardware is undersized.