Lift Inputs
Example Data Table
| Scenario | Units | Load | Legs | Angle | Dynamic | Efficiency | Required WLL each |
|---|---|---|---|---|---|---|---|
| Typical site pick | Metric | 1200 kg | 2 | 60° from horizontal | 1.10 | 0.95 | ≈ 38.0 kN |
| Low angle lift | Metric | 800 kg | 2 | 30° from horizontal | 1.20 | 0.90 | ≈ 71.6 kN |
| Three-leg spread | Imperial | 5000 lb | 3 | 25° from vertical | 1.10 | 0.95 | ≈ 10269 lbf |
Formula Used
Effective lifted load
EffectiveLoad = (Load × DynamicFactor) ÷ Efficiency
Vertical fraction from sling angle
If angle is from horizontal: VerticalFraction = sin(θ). If angle is from vertical: VerticalFraction = cos(θ).
Leg tension
TensionEach = EffectiveLoad ÷ (Legs × VerticalFraction)
Required working load limit
RequiredWLLEach = TensionEach × SafetyFactor
How to Use This Calculator
- Select your unit system based on site documents.
- Enter the load weight, then choose legs and angle reference.
- Add a realistic dynamic factor for movement and starting.
- Set an efficiency value to reflect your rigging setup.
- Choose a safety factor that matches your practice rules.
- Optionally enter sling WLL and rated crane capacity to check limits.
- Press calculate, then download the CSV or PDF report.
Lift Capacity Planning Article
1) Define the lifted load and attachment method
Start with the true lifted weight, including below-hook devices if they travel with the load. Record pick points, center of gravity, and whether the load can rotate. A small shift in center of gravity can overload one leg even when total weight looks acceptable.
2) Apply a realistic dynamic factor
This calculator multiplies the load by a dynamic factor to reflect starts, stops, and controlled motion. Many projects screen lifts at 1.10–1.30 for routine handling, while higher values may be used for rough conditions. Keep the number defendable and consistent with your lift procedure.
3) Account for rigging efficiency losses
Efficiency represents losses from hardware geometry, sling type, and non-ideal load sharing. Values such as 0.90–0.98 are commonly used for clean setups, while complex rigging may justify lower efficiency. Lower efficiency increases effective load, raising leg tension and required WLL.
4) Respect sling angle effects on leg tension
The vertical fraction is computed using sine or cosine depending on how your angle is measured. As the sling flattens, the vertical share decreases and leg tension climbs rapidly. A change from 60° to 30° from horizontal can roughly double required WLL, even when weight stays the same.
5) Choose an appropriate safety factor
Safety factor scales calculated tension to an allowable working limit. Use site rules and applicable standards for the chosen sling type. Overly small safety factors create hidden risk; overly large factors may force unnecessary redesign. Document the selected value in the lift plan.
6) Check crane capacity at the working radius
Crane capacity is only meaningful when taken from the correct configuration and radius. Enter the rated capacity at the planned radius, then apply a deration factor (often 0.80–0.95) to represent wind limits, setup constraints, or project conservatism. The effective lifted load must remain below the derated allowance.
7) Validate rigging component ratings and inspection status
Compare the required WLL per leg to the marked WLL of each sling and the lowest-rated component in the load path, including shackles, hooks, and master links. Inspection findings, wear, and damage can invalidate ratings. If any component is over limit, redesign before lifting.
8) Communicate assumptions and keep a simple record
Use the CSV and PDF outputs to document inputs, results, and checks. Note the angle reference used, the dynamic and deration factors, and any missing data that requires further review. Clear records improve approvals, briefings, and lessons learned across repeat lifts.
FAQs
1) What does “effective lifted load” mean?
It is the adjusted load after applying dynamic factor and dividing by rigging efficiency. It approximates what the system “feels” during motion, not just the static weight.
2) Which angle reference should I choose?
Choose the reference that matches your field measurement. If you measure the sling above the floor, use “from horizontal.” If you measure from the plumb line, use “from vertical.”
3) Why does a lower sling angle increase tension?
Flatter slings provide less vertical support per leg, so each leg must carry more tension to hold the same weight. The calculator captures this using sine or cosine of the angle.
4) What is a good dynamic factor for routine lifting?
Many teams screen routine, controlled lifts around 1.10–1.30, but the correct value depends on procedure, equipment, and handling conditions. Use your project rules and competent-person guidance.
5) How should I pick a deration factor?
Deration reflects reductions for wind limits, setup restrictions, operator policy, or conservatism. Common screening values range from 0.80 to 0.95, but follow the lift plan and crane chart notes.
6) Can this replace a critical lift plan?
No. It is a screening tool for planning and communication. Critical lifts require engineered review, verified charts, site approvals, and a detailed method statement that addresses stability, travel, and hazards.
7) What if sling WLL or crane capacity is not provided?
The tool will still compute leg tension and required WLL, but it flags the outcome as “Review required.” Add the missing ratings to complete the checks before lifting.
Plan, verify, communicate, and lift safely on every site.