Pulley mechanical advantage calculator
The mechanical advantage of a block and tackle is the number of rope falls supporting the load.
%
Effort needed
588.687 85N
- Ideal effort with no friction
- 500
- Real mechanical advantage
- 3.3974
- Rope to pull through
- 8
- System efficiency
- 84.93 %
Show the working
- Load = 2000
- Supporting rope falls = 4
- Efficiency per sheave = 96
- Distance to lift = 2
- Ideal effort with no friction = 2000 / 4 = 500
- eff = (96/100)^4 = 0.849 347
- Effort needed = 500 / 0.849 347 = 588.688
- Rope to pull through = 2 * 4 = 8
- System efficiency = 0.849 347 * 100 = 84.9347
- Real mechanical advantage = 588.688 > 0 ? 2000 / 588.688 : 0 = 3.397 39
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- ideal effort = load / number of supporting falls
- system efficiency = (per-sheave efficiency)^falls
Friction compounds: four sheaves at 96% each give 85% overall, not 96%.