Pulley Calculator
Enter the load weight and the number of rope segments supporting it to size a block and tackle. The ideal mechanical advantage equals the rope count, so the effort force is the load divided by that number.
How to use the pulley calculator
- Enter the load weight in newtons.
- Count the rope segments that pull up on the load and enter that number.
- Read the effort force, the mechanical advantage and the rope you must pull.
Examples
Three supporting ropes
load = 600 N, supporting ropes = 3
effort = 200 N, MA = 3
Single fixed pulley
load = 600 N, supporting ropes = 1
effort = 600 N, MA = 1
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. More supporting ropes mean a smaller effort force.
How do I count the supporting ropes?
Count only the rope segments pulling up on the movable block that holds the load. The segment you pull on counts only if it also lifts the load.
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, so the work stays the same.
Does a single fixed pulley give an advantage?
No. A single fixed pulley only changes the direction of the force. The mechanical advantage is 1, so the effort equals the load.
Does this account for friction?
No. This is the ideal mechanical advantage. Real pulleys lose force to friction, so the actual effort is a little higher than the ideal value shown.
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