Pulley Advantage Calculator
Lifting effort and rope pull from load weight and rope count.
What it does
Pulleys trade force for distance. Reeve a rope over more supporting segments and each segment carries a smaller share of the load, so the hand pulls less. The price is rope: pulling with one third of the force means pulling three times the length.
The tool above runs the ideal block and tackle. Enter the load, count the supporting ropes, and enter the lift height. Effort equals load divided by the rope count, and pull equals lift times the count. The default 600 N on 3 ropes lifting 1.5 m needs 200 N of effort and 4.5 m of rope pull.
University demo labs state the rule the same way. Wisconsin-Madison physics shows effort as load over rope count with pull as lift times count, and UC Santa Barbara demos walk through 1:1, 2:1, 4:1, and 6:1 rigs. Western Washington physics ties advantage directly to the strand count at the load.
Reality adds friction. Every sheave keeps a cut, so a four part purchase with plain bearings can demand a quarter more than the ideal. Fixed single pulleys redirect only, with no advantage at all. Plan anchors for the full load plus the pull side, since both legs load the support.
How to use
- Pick metric (N, m) or imperial (lbf, ft).
- Enter the load weight.
- Count the rope segments supporting the moving block.
- Enter the lift height.
- Read effort first, then rope pull and the ratio.
- Add 10 % or so per sheave for friction in real lifts.
Formula
- Load
- Weight lifted: N in metric mode, lbf in imperial mode.
- n
- Rope segments holding the moving load.
- Lift
- Height the load rises: m or ft.
n counts rope segments supporting the moving load, from 1 to 12. Friction and pulley weight are ignored, so treat results as the ideal floor for effort.
Worked example
Example: 600 N on 3 ropes
Metric defaults: 600 N load, 3 ropes, 1.5 m lift height.
- Inputs: 600 N load, 3 supporting ropes, 1.5 m lift.
- Effort: 600 / 3 = 200 N.
- Rope pulled: 1.5 x 3 = 4.5 m.
- Check: 600 x 1.5 = 900 J equals 200 x 4.5 = 900 J.
- Tool shows 200 N, 4.5 m, 3:1.
Reference table
| Ropes | Effort | Pull for 2 m lift |
|---|---|---|
| 1 (fixed) | Full load | 2 m |
| 2 | Load / 2 | 4 m |
| 3 | Load / 3 | 6 m |
| 4 | Load / 4 | 8 m |
| 6 | Load / 6 | 12 m |
Limits
- Ideal math only. Friction and sheave weight raise real effort.
- Static lifts only. Snatch loads and swinging differ.
- Assumes all segments share evenly, which needs free running blocks.
- Anchor and rope strength checks sit outside this page.
Common mistakes
- Counting the dead end wrong and claiming one extra part.
- Expecting a fixed single pulley to multiply force.
- Forgetting pull distance grows with advantage.
- Ignoring friction on long multi sheave purchases.
- Anchoring to supports rated below load plus pull.
Try it yourself
Quick checks. Answers sit tucked under each question.
100 N, 4 ropes, 2 m lift?
Effort 100 / 4 = 25 N. Pull 2 x 4 = 8 m.
135 lbf, 3 ropes, 5 ft lift?
Effort 135 / 3 = 45 lbf. Pull 5 x 3 = 15 ft.
Questions
What counts as a supporting rope?
The count of rope segments holding the moving load. Two segments halve the effort; four cut it to a quarter.
Is real effort higher than ideal?
It runs higher. Friction in every sheave adds effort, so real systems beat the ideal by 5 to 15 % per pulley.
Do I pull more rope with more pulleys?
No. Rope pulled grows by the same factor the effort shrinks, so work stays constant. Pull 4.5 m to lift 1.5 m at 3:1.
What does a single fixed pulley do?
It redirects only. The pull turns the corner while effort and distance stay equal, minus friction.
Does the anchor point matter?
About half, since one of the two segments anchors. A gun tackle with the rope anchored above roughly doubles advantage over the same blocks hung freely.
What is the quick mental version?
Divide the load by the rope count for effort and multiply the lift by it for pull. With 100 N on 4 ropes lifting 2 m: 25 N and 8 m.
Sources
- UW Madison Physics Museum: Pulleys
- UC Santa Barbara Physics Lecture Demos: Small pulleys
- UC Santa Cruz Physics Demo: Pulley Mechanical Advantage