Rope Rescue Mechanical Advantage

Theoretical and actual MA across rig types with pulley losses.

Run the calculator

Example

You enter

Rig 4:1
Pulley efficiency (0-1) 0.9
Load (lb) 600

You get

Theoretical MA 4
Actual MA (after pulley losses) 2.916
Haul force 206 lb
Pulleys 3

Details, formula, and sources

Theoretical MA per rig type × pulley_efficiency^n_pulleys. Haul force = load / actual_MA. Common rigs 1:1, 2:1, 3:1, 4:1 (Z-rig), 5:1 piggyback, T-method.

NFPA 1006 / NFPA 1670 by name; CMC Rope Rescue Manual + Rigging for Rescue training materials by name.

NFPA standards read-only at nfpa.org/freeaccess; NFA rope-rescue materials free at usfa.fema.gov.

Estimate. AHJ and licensed fire protection engineer govern.

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

Pulley efficiency 0.90 prussik-minding pulley / 0.95 ball-bearing pulley unless user suppliesmanufacturer typical