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Pulley Mechanical Advantage Calculator

Find a pulley system's mechanical advantage.

How it is calculated

The tool applies the ideal-pulley rule: MA = n and F = W / MA. n is the number of rope segments that support the moving load (count the rope parts that pull on the moving block, including the one you pull on only if it ends at the moving block). W is the load in newtons (N) and F is the effort force in newtons.

The segment count is rounded to a whole number and must be at least 1; the load cannot be negative. Friction, rope weight and the weight of the blocks are ignored, so a real system needs more effort than shown. The trade-off is distance: you must pull n times as much rope as the load rises.

Worked example

A load of 800 N is hung from a system with 4 supporting rope segments. The mechanical advantage is 4. The effort is 800 ÷ 4 = 200.00 N. In practice you would also pull 4 metres of rope to lift the load 1 metre, and friction would raise the force you actually need above 200 N.

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Common mistakes

  • Counting pulleys instead of supporting rope segments. A fixed pulley has MA = 1 however many you add; only the rope parts attached to the moving load count.
  • Counting the rope you pull on when it runs off a fixed pulley. That segment redirects force but does not support the load.
  • Entering the load in kilograms. The tool expects newtons; multiply kilograms by about 9.81 first.
  • Expecting the exact effort in practice. The result is ideal and ignores friction, so plan for noticeably more.
  • Forgetting that less force means more rope. With MA = 4, lifting 1 m needs 4 m of rope pulled through.

Sources

About this calculator

For an ideal pulley system, mechanical advantage equals the number of rope segments supporting the moving load — not the number of pulleys. A single fixed pulley has an MA of 1 (it only changes direction), while a block-and-tackle with two segments supporting the load doubles the force, and effort required = load ÷ MA when friction is ignored.

Riggers and crane operators use this to plan how many parts of line a lift needs, sailors size block-and-tackle purchases on halyards and mainsheets the same way, and it's a standard physics-class demonstration of simple machines trading distance for force — pulling more rope through the system to lift a heavier load with less effort.

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Comments (1)

  • Editorial team

    The tool gives the ideal effort only, and it does not check what the anchor point, rope or hardware can carry, which is a separate question and can be higher than the load itself. Look up ratings for each part before relying on any lift. The distance trade-off is easy to test: with 4 segments, lifting 1 m means pulling 4 m of rope. Is your setup for a workshop, a boat or a physics class?

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