Calculator
Example data table
| Radius (cm) | RPM | Acceleration (m/s^2) | g-force (g) | RCF (x g) |
|---|---|---|---|---|
| 8 | 6 | 31582.734 | 3220.543 | 322 |
| 10 | 12 | 157913.67 | 16102.713 | 16099 |
| 6.5 | 15 | 160381.072 | 16354.318 | 16351 |
| 12 | 9 | 106591.728 | 10869.331 | 10867 |
Values are computed using standard centrifuge relationships for quick comparison.
Formula used
- Angular velocity: omega = 2*pi*RPM/60
- Centripetal acceleration: a = omega^2 * r
- g-force: g = a / 9.80665
- RCF approximation: RCF = 1.118e-5 * r(cm) * RPM^2
The RCF form is widely used in laboratory practice because it directly links rotor radius in centimeters with RPM.
How to use this calculator
- Select the calculation mode that matches your known values.
- Enter positive numbers for speed, radius, or force targets.
- Choose radius units carefully, especially for short radii.
- Press Calculate to see acceleration, g-force, RPM, and RCF.
- Use the download buttons to save the latest result.
Article
Understanding Centrifugal Acceleration
Centrifuges create radial acceleration that pushes particles outward while the liquid remains in rotation. This calculator reports acceleration in m/s^2, g-force, and the common laboratory metric RCF (x g). It helps translate protocols between different rotors and clarifies what your settings produce today.
Key Inputs: Radius and Speed
Radius is the distance from the rotation axis to the sample, not the rotor edge. A larger radius increases acceleration linearly. Doubling radius doubles acceleration, while speed changes have a stronger effect because they are squared. Always match the radius to your rotor chart and tube position.
Converting RPM to Angular Velocity
When you enter RPM, the tool converts it to angular velocity using omega = 2*pi*RPM/60. For example, 12,000 rpm corresponds to about 1,256.64 rad/s. Angular velocity is useful for engineering calculations and for comparing different drive systems.
From Acceleration to g-force and RCF
After computing a = omega^2*r, the calculator divides by 9.80665 to show g-force. It also evaluates RCF = 1.118e-5*r(cm)*RPM^2, a standard approximation used on rotor charts and protocol sheets. Rounding can cause differences.
Typical Ranges in Laboratory Rotors
Microcentrifuges often run around 10,000 to 15,000 rpm with radii near 6 to 9 cm, producing roughly 6,000 to 20,000 x g depending on the rotor. Swing-bucket rotors may run 3,000 to 6,000 rpm with 12 to 20 cm radii for gentler pelleting. Ultracentrifuges can exceed 50,000 rpm and reach 100,000 x g or more, but only with approved rotors.
Sensitivity and Error Checks
Because RPM is squared, a 5% RPM increase raises RCF by about 10.25%. Small radius mistakes also matter: entering 8 cm instead of 10 cm lowers RCF by 20%. Use the backward modes to solve the RPM needed for a target RCF, then compare that RPM with your instrument limits. If results look extreme, recheck units and decimal placement.
Practical Setup and Safety Notes
Balance tubes by mass, confirm rotor limits, and use the correct radius for your adapter and tube size. If a protocol specifies RCF, prefer RCF mode to avoid mismatch across different rotors. Record temperature, run time, and brake settings because they affect pellet quality. Save outputs using the CSV or PDF export options for traceable lab notes.
FAQs
1) What is the difference between g-force and RCF?
Both express acceleration relative to gravity. g-force uses a/9.80665 from the physics equation. RCF is the lab-friendly form using radius in centimeters and RPM squared.
2) Which radius should I enter?
Use the effective radius from the axis to the sample location. Check your rotor manual for minimum, maximum, or average radius, and match what your protocol specifies.
3) How do I convert a protocol written in RPM to RCF?
Select the RPM and radius mode, enter RPM and your rotor radius, and read the RCF output. This helps standardize runs across different centrifuges and rotors.
4) Why does my RCF differ from a chart or instrument display?
Differences come from using a different radius value, rounding, or a chart that assumes a specific rotor position. Recheck radius units and verify whether the chart uses maximum or average radius.
5) Can the calculator solve the RPM needed for a target RCF?
Yes. Choose the “RPM from target g-force and radius” mode for g targets, or use “RPM and acceleration from RCF and radius” for RCF targets.
6) What safety checks should I do before a run?
Confirm rotor and tube ratings, inspect for damage, tighten the lid correctly, and balance opposing buckets or tubes by mass. Never exceed the manufacturer RPM limit for that rotor.