RPM — Definition, Formula & Examples

RPM

Revolutions per minute. A unit for measuring speed of rotation.

Key Formula

\text{RPM} = \frac{\text{number of revolutions}}{\text{time in minutes}}

Where:

$\text{number of revolutions}$ = Total count of complete rotations the object makes
$\text{time in minutes}$ = The elapsed time measured in minutes

Worked Example

Problem: A bicycle wheel completes 600 full rotations in 2 minutes. What is the wheel's speed in RPM?

Step 1: Identify the number of revolutions and the time.

\text{revolutions} = 600, \quad \text{time} = 2 \text{ min}

Step 2: Divide the total revolutions by the time in minutes.

\text{RPM} = \frac{600}{2} = 300

Answer: The wheel spins at 300 RPM, meaning it completes 300 full rotations every minute.

Why It Matters

RPM connects rotation to other useful quantities. If you know the RPM and the radius of a wheel, you can calculate the linear speed of a vehicle. RPM also converts directly to angular velocity in radians per second, which is essential in physics and engineering problems involving circular motion.

Common Mistakes

Mistake: Confusing RPM with angular velocity in radians per second.

Correction: RPM counts full turns per minute, while angular velocity is typically measured in radians per second. To convert, use

\omega = \text{RPM} \times \frac{2\pi}{60}

Related Terms

Angular Velocity — Rotation speed measured in radians per second
Circumference — Distance traveled per revolution of a circle
Unit Rate — RPM is a rate per one minute
Radian — Angle unit used in angular velocity conversion