Pulley System Mechanical Advantage

Theoretical and actual MA across fixed/movable/block-and-tackle rigs.

Run the calculator

Example

You enter

Rig block_3
Pulley efficiency (0-1) 0.95

You get

Theoretical MA 3
Actual MA 2.57
Pulleys 3

Details, formula, and sources

Theoretical MA = number of supporting rope segments. Actual MA = theoretical × pulley_efficiency^n_pulleys. Fixed pulley redirects but does not multiply force; movable pulley × 2; block-and-tackle = 2n for n sheaves.

Classical mechanics; NFPA 1006 / 1670 by name for rescue context.

Mechanics texts free at university OCW.

Estimate. AHJ and licensed professional govern.

Field names used by the API: rig, efficiency, theoretical_ma, actual_ma, pulleys

Default pulley efficiency 0.95 ball-bearing / 0.90 prussik-mindingmanufacturer typical