Pulley System Calculator
The effort needed to lift a load with a pulley system, how much rope you pull for each metre of lift, and the mechanical advantage — ideal and with friction.
In a block and tackle the load hangs from several segments of the same rope, and each carries an equal share of the tension.
How the pulley system calculator works
In a block and tackle the load hangs from several segments of the same rope, and each carries an equal share of the tension. The ideal mechanical advantage is the number of rope segments supporting the moving block; the effort is the load divided by that number, and the rope pulled is that number times the lift. Sheave friction eats a little of it — a few percent per pulley.
Formula: MA = n; effort = load ÷ (n × efficiency); rope pulled = n × lift
Worked examples
| Inputs | Effort needed (N) | Note |
|---|---|---|
| 200 kg on 4 segments at 90% | 544.8 | 545 N, 12 m of rope |
| A single fixed pulley | 516.1 | 516 N — no advantage, only direction |
| 500 kg engine on a 6:1 rig | 961.4 | 961 N |
FAQFrequently asked questions
How do I count the rope segments?
Count the lengths of rope that run up from the moving block (the one attached to the load), including the one you pull if it goes upward from that block. A single fixed pulley has one segment — it only changes direction.
Why does the rope pay out so much?
Energy is conserved: a quarter of the force must act over four times the distance. A 4:1 system lifts one metre for every four metres hauled.
What efficiency should I use?
Ball-bearing sheaves lose 2–5% each, plain bushings 10% or more, and the losses compound through the system. 90% is fair for a good four-sheave rig; rescue and rigging tables give figures per sheave.
What about a hoist with a winch?
The same arithmetic applies; the winch supplies the effort. Check the winch’s rated line pull against the effort row, not against the load.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Physical Laboratory — the UK's national measurement institute
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.