Pulley Ratio Calculator

A pulley ratio calculator, which is based on the principles of a pulley system, helps you find the speed ratio of two pulleys. It uses the size of the driver and driven pulley. You can also find the driven RPM if you know the driver RPM.

This tool makes pulley math quick and easy. You don't need to solve long equations by hand. Just enter the pulley sizes and let the calculator do the work.

For more complex systems, consider using a motor gearbox ratio calculator to find the right gear ratio, which also supports mm, cm, and inches. It converts the sizes to one unit before it finds the ratio. This helps keep the result right.

Pulley Ratio Formula

The main pulley ratio formula is:

Pulley Ratio = Driven Pulley Diameter ÷ Driver Pulley Diameter

Here:

• Driver pulley = The pulley that gives the drive.
• Driven pulley = The pulley that gets the drive.

For speed, use this formula:

Driven RPM = (Driver RPM × Driver Pulley Diameter) ÷ Driven Pulley Diameter

The key rule is simple. A large driven pulley gives lower speed. A small driven pulley gives higher speed.

Think of it like bike gears. A big gear can slow the output. A small gear can make the output turn faster.

For an ideal belt drive, we assume no belt slip. The pulley size also refers to the proper working or pitch diameter for the belt type.

How to Use Online Pulley Ratio Calculator

Using our pulley ratio calculator is simple. Follow these steps:

1. Enter the driver pulley diameter.
2. Select the right unit. You can choose mm, cm, or inches.
3. Enter the driven pulley diameter.
4. Add the driver RPM if you want to find the driven RPM.
5. Click the calculate button. The tool will show the pulley ratio and output speed when RPM is given.

The calculator first changes both pulley sizes to mm. It then finds the pulley ratio. If you enter RPM, it also finds the driven speed.

Example Pulley Ratio Calculation

Let's say the driver pulley is 100 mm. The driven pulley is 200 mm.

Use the pulley ratio formula:

Pulley Ratio = Driven Diameter ÷ Driver Diameter

Pulley Ratio = 200 ÷ 100

Pulley Ratio = 2

So, the pulley ratio is 2:1.

Now, let's say the driver runs at 1,750 RPM.

Use the speed formula:

Driven RPM = (Driver RPM × Driver Diameter) ÷ Driven Diameter

Driven RPM = (1,750 × 100) ÷ 200

Driven RPM = 875 RPM

So, the driven pulley turns at 875 RPM.

The larger pulley cuts the speed in half. That's the basic idea behind a pulley speed ratio.

Final Verdict

A pulley ratio calculator saves time and cuts down on math errors. It helps you find the pulley ratio with ease. You can also check the driven RPM for a belt drive system.

Just enter the driver and driven pulley sizes. Add the driver RPM when needed. The tool does the rest.

For the best result, use the correct pulley diameter for your belt system. Also, remember that real drives may have some belt slip.

FAQs

How to calculate pulley ratio?

Divide the driven pulley diameter by the driver pulley diameter.

Pulley Ratio = Driven Diameter ÷ Driver Diameter

For example, 200 mm ÷ 100 mm gives a ratio of 2:1.

What does a 2:1 pulley ratio mean?

A 2:1 ratio means the driven pulley is twice the size of the driver pulley. The driven shaft turns at half the driver speed in an ideal belt drive.

How do I calculate driven RPM?

Use this formula:

Driven RPM = (Driver RPM × Driver Diameter) ÷ Driven Diameter

Does pulley size affect speed?

Yes. A larger driven pulley lowers output speed. A smaller driven pulley raises output speed.

Can I use different units?

Yes. Our calculator supports mm, cm, and inches. It converts the values before it does the math.

Is the pulley ratio formula always exact?

The formula is exact for an ideal belt drive with no slip. Real systems may show small differences due to belt slip and other factors.

What is the difference between driver and driven pulley?

The driver pulley gets power from the motor or engine. The driven pulley receives that power through the belt.