Quick answer: RPM tells you how fast the rotor turns; RCF tells you the force applied relative to gravity. Because RCF depends on both RPM and rotor radius, use × g when transferring a protocol between different centrifuges or rotors.
The standard relationship is RCF = 1.118 × 10⁻⁵ × r × RPM², where r is the rotational radius in centimeters. At 10,000 rpm with an 8 cm radius, the force is about 8,944 × g.
Both a mini centrifuge and a high-speed centrifuge can display high rpm, but their rotors may produce different RCF and accept different tubes.
In this guide:
- What RPM and RCF measure
- How to transfer a protocol
- How to balance correctly
- When to stop a run
RPM and RCF Are Not Interchangeable
| Parameter | Meaning | Best use |
|---|---|---|
| RPM | Revolutions per minute | Operating a specified rotor |
| RCF (× g) | Force relative to gravity | Comparing or transferring methods |
A small change in rpm can cause a larger change in RCF because speed is squared in the formula.
Protocol Transfer
- Find the original protocol’s RCF and time
- Confirm the new rotor’s maximum RCF and tube rating
- Enter the target RCF directly or calculate the required rpm from the new radius
- Match temperature and braking conditions when relevant
- Validate recovery, pellet quality, or separation before routine use
Correct Balancing
- Place equal masses at equal radii opposite each other
- Use the same tube, cap, adapter, material, and fill condition
- Use a balance tube when sample numbers or volumes differ
- Follow the rotor diagram for three or more loads
- Balance buckets and adapters as complete assemblies
Symmetry is not enough if opposing masses differ. High-speed imbalance can damage the rotor, spindle, bearings, samples, and instrument.
Stop and Investigate
- Unexpected vibration
- Knocking, scraping, or rising noise
- Tube leakage
- Rotor or lid fault
- Persistent imbalance alarm
Do not hold, slow, or open a moving rotor by hand. Wait for a complete stop and follow the manual and laboratory SOP.
Frequently Asked Questions
Why do two centrifuges give different results at the same rpm?
Their rotor radii or geometries may differ, producing different RCF and sedimentation paths.
Can water be used in a balance tube?
Often yes when compatible, but follow the method, tube rating, and biosafety SOP. Balance by total mass.
Is maximum RCF always the best setting?
No. Use the force and time validated for the sample. Excess force can damage samples or tubes.
Key Takeaway
Record rotor, RCF, time, temperature, and brake settings together so another laboratory can reproduce the method.
