Calculate winch capacity, first-layer line pull, or cable layer from any 2 inputs using a 10% per layer rule of thumb in lbf, kgf, or N.
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Winch Capacity Formula
The calculator uses a 10% per cable layer rule of thumb. Each layer above the first layer reduces effective line pull by about 10%.
WC = LP * (1 - (CL - 1) * 0.1)
LP = WC / (1 - (CL - 1) * 0.1)
CL = (1 - (WC / LP)) / 0.1 + 1
- WC = winch capacity at the selected cable layer
- LP = line pull on the 1st layer
- CL = cable layer number
- 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 estimates the cable layer that matches that reduced capacity.
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 | Approximate capacity 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 converts forces to pounds-force before calculating, then converts the result back to your selected unit.
| Unit | To lbf | From lbf |
|---|---|---|
| lbf | 1 | 1 |
| kgf | 1 kgf = 2.20462 lbf | 1 lbf = 0.453592 kgf |
| N | 1 N = 0.224809 lbf | 1 lbf = 4.44822 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.
WC = 12000 * (1 - (3 - 1) * 0.1)
WC = 12000 * 0.8 = 9600 lbf
The estimated winch capacity at the 3rd layer is 9,600 lbf.
Example 2: Find the required 1st-layer line pull
Suppose you need 7,000 lbf of capacity on layer 4.
LP = 7000 / (1 - (4 - 1) * 0.1)
LP = 7000 / 0.7 = 10000 lbf
The required 1st-layer line pull is 10,000 lbf.
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 a rule of thumb. Actual winch capacity depends on drum diameter, cable diameter, motor torque, gearing, friction, and the winch design. Use the winch manufacturer’s line pull chart when you need exact capacity values.
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.
