Pulley Ratio Calculator

Pulley ratio calculator for lifting loads and estimating pulling force

A pulley ratio (also called mechanical advantage) tells you how much a pulley system reduces the force you need to lift a load. If you are setting up a block-and-tackle, hoist, or simple rope-and-pulley lift, the practical question is usually not academic. It is whether you can lift the load by hand, whether you need a winch, and how much rope you will have to pull to raise the load by a given height.

This calculator is locked to one job: estimating lifting effort from a known load and a known number of supporting rope segments (parts of line). It is not for belt drives, gear ratios, timing pulleys, or speed reduction in rotating machines. For lifting systems, the “ratio” is driven by how many rope segments directly support the moving block. More supporting segments generally means less pulling force, but you trade that for more rope travel.

Start by entering the load in kilograms and the number of supporting rope segments. The result shows the ideal mechanical advantage, an adjusted mechanical advantage using an efficiency estimate, and the pulling force required. If you add a lift height, the calculator also shows how much rope you need to pull and gives a simple work/energy check so you can sanity-test the numbers. The outputs are designed for quick decisions: can a person pull it, do you need two people, or is it in winch territory.

Assumptions and how to use this calculator

• This is for lifting loads with a rope-and-pulley system where the ratio is based on supporting rope segments, not rotating pulley speed ratios.
• Load is treated as a static lift (no acceleration). Starting friction, shock loads, and dynamic lifting are not included.
• Efficiency is a single combined estimate for friction and losses. If you do not know it, a default of 85% is used as a practical midpoint for real setups.
• Mechanical advantage is applied to force only. Rope travel is based on the ideal parts-of-line count, which is the standard way people plan rope length.
• Units are metric. “Pulling force in kg equivalent” is a convenience conversion based on Earth gravity and is not a mass you should physically hang.

Common questions

What does “supporting rope segments” mean?

It is the number of rope sections that directly hold up the moving block attached to the load. Count the strands that run between the moving block and the fixed block or anchor. That count is the ideal mechanical advantage. If you count incorrectly, your force estimate will be wrong.

Why does the calculator ask for efficiency?

Real systems lose force to friction in sheaves, bearings, rope bends, and misalignment. Efficiency collapses those losses into a single adjustment. If you leave it blank, the calculator uses a reasonable default so you still get a usable estimate. If your setup is rough or dirty, expect lower efficiency and a higher pulling force.

Is the pulley ratio the same as “how much easier it feels”?

Not exactly. The ratio predicts steady pulling force, but the “feel” is affected by start-up friction, rope stretch, the angle you pull from, and whether the load is sticking or swinging. Use the result as a baseline and add margin if the lift is awkward or safety-critical.

How much rope do I need to pull to lift the load?

In an ideal system, rope travel scales with the parts of line. If you have 4 supporting segments, lifting the load 1 meter needs roughly 4 meters of rope pulled. This is why higher mechanical advantage makes lifting easier but slower. The lift height input exists to quantify that trade-off.

When will this calculator not apply?

It will not apply to belt and gear pulley ratios, and it will not apply to systems where the rope is not the primary load path (for example, some lever hoists or chain blocks with internal gearing). It is also not a rigging safety calculator. If you are lifting people, working overhead, or operating near capacity, follow manufacturer ratings and proper rigging practices instead of relying on a quick estimate.