Pulley & Sheave Size Calculator
Driven sheave size for a target fan RPM.
Enter your values
Enter the motor sheave diameter in in.
Enter the motor rpm in rpm.
Enter the target fan rpm in rpm.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Driven sheave diameter
- 8.75 in
- Drive ratio
- 1.944:1
- Check fan RPM
- 900 rpm
Quick answer
Driven sheave diameter equals motor sheave diameter multiplied by motor RPM divided by target fan RPM.
D_driven = D_motor x RPM_motor / RPM_fan
At a glance
| What it does | Driven sheave size for a target fan RPM. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Motor sheave diameter, Motor RPM, Target fan RPM |
| Main output | Driven sheave diameter |
| Formula | D_driven = D_motor x RPM_motor / RPM_fan |
| Cost | Free — no sign-up, no download |
How to use the Pulley & Sheave Size Calculator
- 1Enter the motor sheave diameter and motor RPM (usually 1750 or 3450 rpm nominal).
- 2Enter the target fan shaft RPM from the fan curve.
- 3Order the nearest stock driven sheave to the calculated diameter.
Inputs explained
- Motor sheave diameter(in)
- Enter the motor sheave diameter in in.
- Motor RPM(rpm)
- Enter the motor rpm in rpm.
- Target fan RPM(rpm)
- Enter the target fan rpm in rpm.
Worked example
Using the values the calculator loads with:
Inputs
- Motor sheave diameter4.5 in
- Motor RPM1750 rpm
- Target fan RPM900 rpm
Results
- Driven sheave diameter8.75 in
- Drive ratio1.944:1
- Check fan RPM900 rpm
Frequently asked questions
What if only stock sizes are available?
Pick the closest stock size and recompute the resulting fan RPM to check it is acceptable.
Does belt slip affect this?
Assume 1-2% slip for V-belts; synchronous belts have essentially no slip.
What do I need to enter into the Pulley & Sheave Size Calculator?
Just 3 values: motor sheave diameter, motor rpm, target fan rpm. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Pulley & Sheave Size Calculator work out the answer?
Driven sheave diameter equals motor sheave diameter multiplied by motor RPM divided by target fan RPM. It applies the formula D_driven = D_motor x RPM_motor / RPM_fan and shows the working so you can check each step by hand.
Is the Pulley & Sheave Size Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.