Example Data Table
Typical values for quick checks (radius measured to sample position).
| RPM | Radius (cm) | RCF (g) | Use case |
|---|---|---|---|
| 6000 | 8 | 3219 | Cell pelleting in bench centrifuges |
| 12000 | 10 | 16099 | Protein precipitation and spin columns |
| 18000 | 7 | 25322 | Microcentrifuge high-speed clarification |
Formula Used
Relative centrifugal force (RCF) expresses the acceleration at the sample as multiples of Earth’s gravity.
- RCF = ω²r / g, where ω is angular velocity and r is radius.
- ω = 2π × RPM / 60.
- Combining constants gives the lab form: RCF = 1.118e-5 × r(cm) × RPM².
Tip speed is computed as v = ωr with r in meters.
How to Use This Calculator
- Select a mode: compute RCF, RPM, or radius.
- Enter the two known values, using the correct units.
- Press Calculate to display results above the form.
- Use the download buttons to export your latest result.
- For rotor radius, measure from the axis to the sample.
Centrifugation G-Force Guide
Relative centrifugal force (RCF) is the acceleration at your sample expressed in multiples of Earth’s gravity. Because rotors differ in size, RCF is the safest way to reproduce protocols across instruments. This calculator standardizes results using the widely used lab form, RCF = 1.118e-5 × r(cm) × RPM². It also helps verify rotor charts when translating methods between instruments.
Why RCF matters more than RPM
RPM only describes how fast the motor turns. The sample experiences acceleration that depends on both RPM and the distance from the axis. Two rotors spinning at 12,000 rpm can produce very different g forces if their radii differ. Reporting RCF keeps methods comparable.
How radius changes g force
RCF scales linearly with radius. If you move a tube from a 7 cm position to a 10 cm position at the same speed, g force increases by about 43%. For accuracy, measure to the sample location (tube bottom for pelleting) rather than the rotor edge.
RPM squared scaling in practice
RCF scales with RPM squared, so small speed changes matter. Doubling RPM increases g force by four times. Example: at 10 cm radius, 10,000 rpm produces 11,180 g, while 12,000 rpm produces about 16,099 g. Use this to fine-tune protocols.
Typical g ranges by instrument class
General-purpose swing-bucket centrifuges often run around 300–3,000 g for blood separations and gentle pelleting. High-speed fixed-angle units commonly reach 10,000–25,000 g for lysate clearing. Ultracentrifuges can exceed 100,000 g and may approach 1,000,000 g for density gradients.
Matching g force to common workflows
Soft pellets (cells, nuclei) are frequently handled at a few hundred to a few thousand g to reduce damage. Clarification spins for debris removal typically sit in the 10,000–20,000 g range. Always balance g force with time, temperature, and sample fragility to avoid losses. Pair RCF with run time, because separation depends on both.
Tip speed and shear considerations
Beyond g force, tip speed can influence mixing, shear, and heat. This calculator reports tip speed from v = ωr, where ω = 2π×RPM/60. At 15,000 rpm and 7 cm radius, ω is about 1570.8 rad/s and tip speed is roughly 110.0 m/s.
Safety, balancing, and rotor limits
Never exceed the rotor’s rated RPM or maximum RCF, especially as rotor fatigue increases with use. Use matched tube masses, inspect for corrosion, and tighten lids to the specified torque. If your calculation suggests extreme values, re-check radius units and confirm the rotor chart.
FAQs
1) What radius should I enter?
Use the distance from the rotation axis to the sample location. For pelleting, that is usually the bottom of the tube where the pellet forms, not the rim of the rotor.
2) Why do protocols specify RCF instead of RPM?
RCF accounts for rotor radius, so it reproduces acceleration across different centrifuges. RPM alone can under- or over-spin a sample if the rotor geometry changes.
3) Can I compare two rotors using this tool?
Yes. Enter the same RPM with each rotor’s radius to compare RCF, or enter the same target RCF to find the RPM required for each rotor.
4) Is higher g always better?
No. Higher g can compact pellets, damage delicate cells, increase heating, or drive unwanted co-pelleting. Choose the lowest g that achieves separation within an acceptable time.
5) What happens if I change RPM slightly?
Because RCF scales with RPM², a 10% RPM increase raises g force by about 21%. Use small changes carefully, especially near rotor limits or when optimizing sensitive samples.
6) Where does the 1.118e-5 constant come from?
It combines the conversion from RPM to angular velocity and divides by standard gravity while using radius in centimeters. It is the common laboratory simplification of RCF = ω²r/g.
7) Why does tip speed matter if RCF is correct?
Tip speed relates to fluid shear and potential warming. Two setups can share the same RCF but differ in tip speed, which can affect fragile particles, emulsions, and viscous samples.