Convert radial acceleration in multiples of standard gravity to rotational speed when the rotation radius is known, or calculate g-force from RPM.
Radial acceleration in rotating motion depends on angular speed squared and on radius. The calculator expresses that acceleration as a multiple of standard gravity and converts between it and revolutions per minute.
How to Use This Calculator
- Choose RPM from g-force or g-force from RPM.
- Enter the radial acceleration or speed.
- Enter the radius and its unit.
- Calculate and review angular speed or acceleration.
After a successful calculation, the inputs and result remain saved in this browser. Select Reset to clear the stored values and restore the calculator defaults.
How the G-Force to RPM Calculator Works
Enter radius, not diameter. The result describes acceleration at that distance from the axis; it is not a force until mass is included.
The primary relationship is RPM = √(g-force × 9.80665 ÷ radius) × 60 ÷ (2π). Calculations retain full available precision internally; displayed values are rounded for readability.
Formula Variables and Input Guide
Enter radial acceleration or RPM and the distance from the axis to the point of interest.
| Variable or term | Meaning | Unit or note |
|---|---|---|
| a | Centripetal acceleration | m/s² |
| g | Multiple of standard gravity | dimensionless |
| r | Radius from axis | m |
| ω | Angular speed | rad/s |
| RPM | Revolutions per minute | rev/min |
Choosing the Right Inputs
Enter the radius from the axis of rotation to the exact point where acceleration is needed, not the rotor diameter. Select the radius unit carefully before entering the value. Samples extending across a range of radii experience different acceleration, so use the sample location relevant to the procedure or equipment specification.
The g input is a multiple of standard gravity and the RPM input is revolutions per minute under steady rotation. This ideal relationship does not account for ramp-up, vibration, imbalance, or tangential acceleration. Confirm the rotor, adapters, containers, and equipment are rated for the intended speed independently of the calculated radial acceleration.
Practical Uses
- Setting a centrifuge or rotating-test speed.
- Comparing acceleration at different radii.
- Converting an RPM specification into radial g.
- Checking the difference between radius and diameter inputs.
RPM needed for 10 g
| Radius | Approximate RPM |
|---|---|
| 25 mm | 598 RPM |
| 50 mm | 423 RPM |
| 100 mm | 299 RPM |
| 200 mm | 211 RPM |
Understanding Your Results
The calculator returns RPM and angular speed or g-force and acceleration.
Smaller radii require higher RPM to produce the same radial acceleration. Equipment ratings, rotor balance, and sample position must be considered separately.
Worked Example
At a 0.1 m radius, 10 g corresponds to about 299 RPM.
At 300 RPM and a 0.1 m radius, angular speed is 31.416 rad/s. Squaring it and multiplying by 0.1 m gives about 98.70 m/s², or roughly 10.06 g.
Checking the Result by Hand
Convert radius to metres and multiply the entered g value by 9.80665 to obtain m/s². Then calculate angular speed as the square root of acceleration divided by radius, and convert rad/s to RPM with ×60 ÷ 2π. Reverse mode uses acceleration = (2π × RPM ÷ 60)² × radius.
At the same radius, doubling RPM must produce four times the g-force because acceleration depends on speed squared. At the same RPM, doubling radius must double g-force. Those sensitivity checks quickly reveal a radius/diameter or unit mistake.
Common Mistakes to Avoid
- Entering diameter instead of radius.
- Treating g as a force without multiplying by mass.
- Ignoring vibration or tangential acceleration.
- Exceeding the rated speed of rotating equipment.
Assumptions and Limitations
This is centripetal acceleration at one radius under steady rotation. It excludes vibration, tangential acceleration, imbalance, and structural safety factors.
Frequently Asked Questions
Should I enter radius or diameter?
Enter the distance from the axis to the point of interest—one half of diameter.
Is this the same as RCF?
It calculates the same radial-acceleration concept often called relative centrifugal force.
Why does radius change RPM?
Acceleration equals angular speed squared times radius.
Does the result include imbalance?
No. It assumes steady ideal rotation.