| System | n | η (%) | Load (N) | Lift (m) | Effort (N) | Rope pulled (m) | AMA |
|---|---|---|---|---|---|---|---|
| Single Fixed | 1 | 85 | 500 | 2.00 | 588.24 | 2.00 | 0.85 |
| Single Movable | 2 | 85 | 500 | 2.00 | 294.12 | 4.00 | 1.70 |
| Block & Tackle | 4 | 85 | 500 | 2.00 | 147.06 | 8.00 | 3.40 |
| Custom | 6 | 90 | 800 | 1.50 | 148.15 | 9.00 | 5.40 |
- W = m × g (convert mass to load weight)
- IMA ≈ n (n = number of supporting rope segments)
- Effort = W / (IMA × η) where η is efficiency (0–1)
- Rope pulled = Lift height × IMA (velocity ratio ≈ IMA)
- Work out = W × Lift height
- Work in = Effort × Rope pulled
- Efficiency (%) = (Work out / Work in) × 100
- Power = Work / time (when time is provided)
- Select the system type that matches your pulley arrangement.
- Enable auto segments for typical setups, or enter n directly.
- Enter load as mass (kg) or weight (N), and set g if needed.
- Set efficiency to reflect friction and rope/pulley condition.
- Enter lift height; optionally add lift time to estimate power.
- Press Calculate to view results above the form.
- Use CSV or PDF export to save calculations for reports.
Mechanical advantage from supporting segments
In an ideal setup, the ideal mechanical advantage (IMA) matches the number of rope segments supporting the moving load. A single fixed pulley typically has n=1, a single movable pulley n=2, and common block-and-tackle rigs use n=4, 6, or 8. With a 500 N load and n=4, the ideal effort is 125 N before losses.
Efficiency modeling for friction and bending
Real pulleys lose energy through bearing friction, rope bending, and sheave misalignment. This calculator applies an overall efficiency η to scale the ideal advantage: Effort = W/(n×η). Field values often range from 70% for rough hardware to 90–95% for well-maintained sheaves. For the same 500 N load, n=4, and η=0.85, the effort rises from 125 N to about 147 N.
Rope travel and speed tradeoffs
Lower effort comes with greater rope travel. The velocity ratio is approximately n, so lifting 2.0 m with n=6 requires pulling about 12.0 m of rope. If your pulling speed is 0.5 m/s, that lift needs roughly 24 s of motion, ignoring pauses. Use the rope pulled output to plan clearance, drum capacity, and operator travel distance. When using a winch, confirm that the free end can move continuously without rubbing on edges, and always allow extra for knots and anchor wraps.
Work, energy, and power outputs
Work out equals W×h and represents the load’s gain in gravitational potential energy. Work in equals effort×rope travel and is higher when efficiency is below 100%. The difference is reported as energy loss. When lift time is entered, the tool estimates output power (W×h/t) and input power (effort×rope/t), helping compare human pulling to motorized hoists.
Practical checks for realistic results
Use the example table to sanity-check your inputs. If calculated effort is below 50 N for a heavy load, your segment count is likely too high or η too optimistic. If results are overly large, verify units, confirm whether load input is mass or weight, and reassess friction. For rigging decisions, treat these numbers as planning estimates and keep additional safety margin.
How do I choose the supporting segments value n?
Count only the rope parts directly holding the moving block or load. Ignore the free end you pull. If unsure, use auto segments for typical fixed, movable, and block arrangements.
Why does my effort not equal load divided by n?
The calculator applies efficiency to represent friction and bending losses. Effort increases as efficiency decreases, even if n stays the same.
Should I enter load as mass or weight?
Use mass (kg) when you know the object’s mass, and the tool converts using g. Use weight (N) when a force reading or specification already gives Newtons.
What does rope pulled mean in practice?
It is the approximate distance the free end must move to raise the load by the lift height. Higher n reduces effort but multiplies pulling distance and time.
Is the rope tension the same everywhere?
This tool reports an approximate segment tension near the pulling end. Real tension varies with friction, angle changes, and pulley quality, so treat it as an estimate.
Can I use this for safety-critical lifting plans?
Use it for planning, education, and quick comparisons. For critical lifts, follow local safety rules, verify hardware ratings, and consult qualified rigging professionals.