Pulley Calculator
This pulley calculator sizes an ideal block and tackle from two numbers: the weight you want to lift and how many rope segments support it. The ideal mechanical advantage equals that rope count, so the effort force is simply the load divided by the number of supporting ropes. It also reports how much rope you must haul in for every unit the load climbs.
How to use the pulley calculator
- Enter the load force in newtons in the Load force field.
- Count only the rope segments pulling up on the movable block and enter that whole number under Supporting ropes.
- Read the effort force you must apply from the first result card.
- Check the mechanical advantage and the rope pulled multiplier in the other two cards.
- Use the copy button to save the effort, mechanical advantage and rope multiplier as one line.
Examples
Three supporting ropes
load force = 600 N, supporting ropes = 3
effort = 200 N, mechanical advantage = 3, rope pulled = 3x distance
Single fixed pulley
load force = 600 N, supporting ropes = 1
effort = 600 N, mechanical advantage = 1, rope pulled = 1x distance
Four rope block and tackle
load force = 1000 N, supporting ropes = 4
effort = 250 N, mechanical advantage = 4, rope pulled = 4x distance
Frequently asked questions
How does a pulley's mechanical advantage work?
In an ideal block and tackle the mechanical advantage equals the number of rope segments that support the load. Each supporting segment shares the weight, so more ropes mean a smaller effort force at the free end.
How do I count the supporting ropes?
Count only the rope segments that pull up on the movable block holding the load. The segment you haul on counts too, but only when it also runs up to lift the load rather than just changing direction.
Why do I pull more rope than the load rises?
A pulley trades distance for force. With N supporting ropes you pull N times as much rope as the height the load rises, which is why the tool reports rope pulled as an N times multiplier. The total work stays the same.
Does a single fixed pulley give an advantage?
No. A single fixed pulley only redirects the force, for example letting you pull down to lift up. Its mechanical advantage is 1, so the effort equals the full load, as the single rope example shows.
Does this account for friction?
No. It reports the ideal mechanical advantage with frictionless pulleys. Real sheaves lose force to friction and rope stiffness, so the effort you actually apply is somewhat higher than the ideal figure here.
What units does it use?
The load and the effort are both in newtons, and the mechanical advantage and rope multiplier are unitless ratios. To convert a mass in kilograms to a load in newtons, multiply by about 9.81.
Can the number of supporting ropes be a decimal?
No. Rope segments are counted as whole numbers, so the tool requires a positive integer of at least 1. Entering a fraction or zero shows a prompt to fix the rope count.
Is this the same as a wheel and axle or gear ratio?
No. This model is specific to block and tackle pulley systems where advantage comes from rope segments. Wheel and axle setups and gear trains gain advantage from radius or tooth ratios instead, which need a different calculation.
Does anything get uploaded?
No. The math runs in your browser, so your load figures stay on your device with nothing sent to a server.
Learn more
- Block and tackle mechanical advantage explained
How rope segments multiply your lifting force, why you trade distance for force, and where real pulleys fall short of the ideal.
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