Convert Relative Centrifugal Force (×g) to RPM
Use this centrifuge calculator to find the rotor speed (RPM) needed to achieve your target RCF (×g).
Why convert g to RPM?
In centrifugation, protocols are often written in RCF (relative centrifugal force, expressed as ×g), while many centrifuges are set using RPM (revolutions per minute). Because rotor size differs between machines, one RPM value does not produce the same force on every centrifuge. Converting from g to RPM ensures your sample experiences the correct force and gives reproducible results.
Key concept: radius changes everything
The force created in a centrifuge depends on both spin speed and rotor radius. A larger radius produces more force at the same RPM. That means:
- Two centrifuges at 6,000 RPM can generate different RCF values.
- You must use your specific rotor radius when converting.
- Protocol accuracy improves when you report RCF and rotor type.
How to use this g to RPM calculator
- Enter your target centrifugal force in ×g.
- Enter rotor radius (distance from axis to sample).
- Choose radius unit (cm, mm, or inches).
- Click Calculate RPM.
The tool instantly returns the required speed. For practical operation, round to a value your centrifuge can set and confirm you remain within rotor safety limits.
Example calculation
If you need 3,000 ×g with a rotor radius of 8 cm, the required speed is approximately 5,790 RPM. If another rotor has radius 12 cm, the RPM needed for 3,000 ×g is lower. This is exactly why direct RPM comparisons across centrifuges are unreliable.
Quick reference (approximate values at 8 cm radius)
| Target RCF (×g) | Approximate RPM |
|---|---|
| 500 ×g | 2,364 RPM |
| 1,000 ×g | 3,343 RPM |
| 3,000 ×g | 5,790 RPM |
| 5,000 ×g | 7,478 RPM |
| 10,000 ×g | 10,576 RPM |
Common mistakes to avoid
- Using tube length instead of rotor radius: radius is measured from rotor center to sample position.
- Mixing units: ensure mm/inches are converted correctly to cm.
- Copying RPM from someone else’s protocol: always verify against your rotor.
- Ignoring rotor max RPM: never exceed the manufacturer limit.
Practical tips for better centrifugation results
1) Record both RCF and rotor information
Storing the force target and rotor radius in your lab notes makes methods portable and easy to reproduce.
2) Balance tubes carefully
Even with the right RPM, imbalanced loads can reduce separation quality and damage equipment.
3) Check rotor condition regularly
Cracked, corroded, or worn rotors can fail at high speed. Follow inspection and retirement schedules.
FAQ
Is g the same as RCF?
In centrifuge protocols, “g” usually means RCF in multiples of Earth gravity (×g).
Can I use this for microcentrifuges and larger floor models?
Yes. The formula is universal as long as radius is entered correctly and within rotor operating limits.
Should I use minimum, average, or maximum radius?
For complete pelleting, many labs use maximum radius. For strict protocol matching, follow your method’s specified radius convention.
Bottom line
A reliable g to RPM conversion is essential for reproducible centrifugation. Use target RCF, correct rotor radius, and safe speed limits every time. The calculator above gives a fast, accurate RPM estimate so your protocol stays consistent across different centrifuges.