Choose a result to evaluate an illustrative linear 10% per added-layer model in lbf, kgf, or N. Manufacturer ratings remain the authority for actual available pull.
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Winch Capacity Formula
The calculator assumes each added rope layer removes ten percentage points of the first-layer pull. This illustrative linear assumption is not a universal winch-capacity rule and is not a compounded 10% reduction.
- WC = winch capacity at the selected cable layer
- LP = line pull on the 1st layer
- CL = rope layer number, or a continuous equivalent index when solved inversely. A fractional index is not a physical full layer.
- 0.1 = 10% reduction per additional cable layer
If you enter line pull and cable layer, the calculator finds winch capacity at that layer.
If you enter winch capacity and cable layer, it rearranges the formula to estimate the required 1st-layer line pull.
If you enter line pull and winch capacity, it finds the algebraic equivalent layer index matching the assumed reduction.
The calculator converts lbf, kgf, and N internally so the force units can be mixed between the input and output fields.
Capacity Reduction by Cable Layer
This table shows the reduction factor used by the calculator. It is based on the simplified 10% per layer rule.
| Cable layer | Formula factor | Assumed first-layer pull remaining |
|---|---|---|
| 1 | 1.00 | 100% |
| 2 | 0.90 | 90% |
| 3 | 0.80 | 80% |
| 4 | 0.70 | 70% |
| 5 | 0.60 | 60% |
Force Unit Conversion Factors
The calculator uses exact force definitions internally and converts to the selected output unit. The table below gives rounded equivalents.
| Unit | To lbf | From lbf |
|---|---|---|
| lbf | 1 | 1 |
| kgf | 1 kgf ≈ 2.20462 lbf | 1 lbf = 0.45359237 kgf |
| N | 1 N ≈ 0.224809 lbf | 1 lbf = 4.4482216152605 N |
Example Calculations
Example 1: Find winch capacity on the 3rd layer
Suppose the 1st-layer line pull is 12,000 lbf and the cable is on layer 3.
The illustrative model gives 9,600 lbf at the 3rd layer; check the manufacturer’s chart for actual capacity.
Example 2: Find the required 1st-layer line pull
Suppose you need 7,000 lbf of capacity on layer 4.
The assumed model implies a first-layer pull of 10,000 lbf; this alone does not select a suitable winch.
FAQ
Why does winch capacity decrease on higher cable layers?
As more cable wraps onto the drum, the effective drum diameter gets larger. A larger drum radius reduces the pulling force the winch can apply. This is why a winch usually has its highest rated pull on the 1st layer.
Is the 10% per layer rule exact?
No. It is an illustrative assumption. Actual pull depends on drum and rope diameter, torque, gearing, friction and spooling. Use the specific manufacturer’s pull-by-layer chart and rating conditions; some winches are rated on a layer other than the first. Observe required minimum wraps and rigging limits. This calculator does not authorize lifting or personnel use.
Can winch capacity at a layer be higher than the 1st-layer line pull?
No. Under this formula, capacity can only stay the same on layer 1 or decrease on higher layers. If your entered winch capacity is higher than the 1st-layer line pull, the inputs do not match this model.
