Multiple Pulley RPM Calculator

A multiple pulley RPM calculator helps you find the final speed of a pulley system. It uses the input motor RPM and the diameter of each driver and driven pulley.

This tool is useful for belt drives, machines, fans, pumps, conveyors, and other rotating equipment. You can also use it as a two pulley RPM calculator or a multi-stage pulley ratio calculator.

The basic idea is simple. A small driver pulley makes a larger driven pulley turn slower. A larger driver pulley makes a smaller driven pulley turn faster.

Our online calculator applies this rule to each pulley stage. The output RPM from one stage becomes the input RPM for the next stage.

Multiple Pulley RPM Formula

The main pulley RPM calculation formula is:

Nout = Nin × (Ddriver ÷ Ddriven)

Where:

• Nout = output pulley speed in RPM
• Nin = input pulley speed in RPM
• Ddriver = driver pulley diameter
• Ddriven = driven pulley diameter

For several pulley stages, use:

Nfinal = Ninput × (D1 ÷ D2) × (D3 ÷ D4) × (D5 ÷ D6)

For the overall pulley ratio:

Overall Ratio = (D2 ÷ D1) × (D4 ÷ D3) × (D6 ÷ D5)

Then:

Nfinal = Ninput ÷ Overall Ratio

This formula is ideal for an electric motor RPM pulley calculator, belt pulley RPM calculator, and pulley-to-pulley RPM calculator.

The calculator can accept pulley diameters in mm, cm, or inches. Since the driver and driven diameters use the same unit, the unit cancels in the ratio.

How to Use Online Multiple Pulley RPM Calculator

1. Enter the motor or input speed in RPM. This is the starting pulley speed.
2. Select the pulley diameter unit. You can use mm, cm, or inches.
3. Enter the driver and driven pulley diameters for the first stage.
4. Add the next pulley stages and enter their driver and driven diameters.
5. Click calculate. The calculator finds each stage RPM, the overall pulley ratio, and the final RPM.

The result shows how the speed changes from the first pulley to the final pulley. This makes it easy to check a pulley ratio RPM calculator result.

Example Multiple Pulley RPM Calculation

Suppose an electric motor runs at 1,800 RPM.

The first stage has a 100 mm driver pulley and a 200 mm driven pulley. The second stage has an 80 mm driver pulley and a 240 mm driven pulley.

First, calculate Stage 1:

Nout = 1,800 × (100 ÷ 200)

Nout = 900 RPM

Now use 900 RPM as the input for Stage 2:

Nout = 900 × (80 ÷ 240)

Nout = 300 RPM

Therefore, the final pulley speed is:

Final RPM = 300 RPM

The overall ratio is:

Overall Ratio = (200 ÷ 100) × (240 ÷ 80)

Overall Ratio = 2 × 3

Overall Ratio = 6:1

So, this pulley system reduces the motor speed from 1,800 RPM to 300 RPM.

Final Verdict

A multiple pulley RPM calculator makes pulley speed calculations fast and simple. Enter the motor RPM, choose the diameter unit, and enter each driver and driven pulley.

The calculator then works through every stage and gives the final RPM and overall pulley ratio.

It can help when calculating pulley size and RPM, checking a belt drive, or planning a machine speed change. The formula assumes an ideal belt drive with no slip.

FAQs

What is a multiple pulley RPM calculator?

A multiple pulley RPM calculator finds the final RPM of a belt-driven system with two or more pulley stages.

How do you calculate pulley RPM?

Use:

Nout = Nin × (Ddriver ÷ Ddriven)

Apply the formula at every pulley stage.

Can I use this as a two pulley RPM calculator?

Yes. For one driver and one driven pulley, simply use the basic pulley RPM formula.

How do you calculate pulley size from RPM?

Rearrange the formula:

Ddriven = Ddriver × (Nin ÷ Nout)

This lets you find the required driven pulley diameter when the desired RPM is known.

Does pulley diameter affect RPM?

Yes. With the same input speed, a larger driven pulley produces a lower RPM. A smaller driven pulley produces a higher RPM.

Does this calculator include belt slip?

No. The calculation uses the ideal pulley diameter ratio and assumes no belt slip or belt creep.