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Pulley Calculator

Free pulley calculator — mechanical advantage from supporting ropes for hoists, lifts and block and tackle, plus rope length and efficiency.

Pulley arrangement

Load force (N)

Lift height (m)

Efficiency (%)

Fill in every field.

Formula

Ideal mechanical advantage (MA) equals the number of rope segments supporting the moving block. Count the segments, not the wheels: a single fixed pulley has one wheel and an MA of 1, because it only redirects your pull. Every extra segment shares the load but adds the same multiple to the rope you must haul.

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Everyday Uses

Rigging a hoist for an engine or a beam

Work out how many parts of line you need before buying blocks, and how much rope that will take. Under-specifying is the usual mistake and an expensive one.

Understanding how a lift really works

The counterweight, not the pulley, does most of the work in a passenger lift. Seeing the numbers explains why lift motors are so much smaller than the car they move.

Sailing hardware

Mainsheet and vang tackles are specified by purchase ratio. Knowing yours tells you whether a loaded sheet can be held by hand or needs a winch.

Rescue and hauling systems

Climbers build 3:1 and 5:1 hauls from slings and pulleys. The rope-length penalty matters as much as the force gain when you have a fixed length to work with.

Sash windows and stage rigging

Counterweighted sashes and theatre fly systems are pulley problems, balanced so a heavy pane or a scenery flat moves with one hand.

Gym cable machines

The plate you select is not always the load you feel. Machines reeved 2:1 halve it, which is why the same number on two different machines is not the same exercise.

Frequently Asked Questions

How do you work out the mechanical advantage of a pulley system?

Count the rope segments that actually pull upward on the moving block — not the number of wheels. A single fixed pulley bolted to a beam has one wheel and a mechanical advantage of 1, because only one segment supports the load and all the pulley does is change the direction of your pull. Add a movable pulley riding on the load and two segments now share it, giving an MA of 2. A block and tackle with three sheaves in each block typically gives 6. This counting rule is what students most often get wrong, and it is essentially the whole topic.

Why does a single fixed pulley give no mechanical advantage?

Because rope tension is the same throughout, and only one length of it is holding the load up. Pulling down on one end produces exactly the load's weight of tension in the other. What you gain is convenience rather than force: you can pull downward using your body weight instead of lifting upward, and you can stand somewhere sensible rather than directly beneath the load. On a flagpole or a well that convenience is the entire point.

How much rope do you have to pull?

Exactly the mechanical advantage multiplied by the height you want to lift. A system with an MA of 4 raising a crate 3 metres needs 12 metres of rope hauled through your hands. This is the trade every simple machine makes, and it has real consequences: a high-advantage tackle needs a great deal of rope, somewhere for that rope to go, and considerably more time per lift. It is one reason cranes use powered winches rather than ever-larger tackles.

How efficient are real pulley systems?

Each sheave costs something. A good sealed-bearing pulley might lose 2 to 5 percent and a plain bushing considerably more, with the losses compounding through the system. A six-part tackle on cheap blocks can easily deliver an actual advantage nearer 4 than 6. Rope stiffness matters too — thick, stiff rope resists bending round a small sheave and wastes effort every time it does. This is why serious rigging uses large-diameter sheaves relative to the rope.

How do lifts and cargo hoists use pulleys?

A passenger lift runs its cables over a driving sheave at the top of the shaft with a counterweight on the other side, so the motor only has to move the difference between car and counterweight rather than the whole load. Cargo hoists and gantry cranes more often use a straightforward block and tackle to trade motor speed for lifting force. In both cases the reeving — how the rope is threaded through the blocks — is chosen to give a specific mechanical advantage for the loads expected.