RCF (×g) ↔ RPM Converter
Use this centrifuge converter to switch between relative centrifugal force (RCF, or ×g) and rotational speed (RPM). Enter your rotor radius and either g-force or RPM, then click the matching button.
RCF (×g) = 1.118 × 10-5 × r(cm) × RPM2
RPM = √(RCF / (1.118 × 10-5 × r(cm)))
What this g rpm converter calculator does
In centrifuge work, protocols often specify speed in one of two ways: RPM or RCF (×g). RPM is simply how fast the rotor spins. RCF describes the actual force the sample experiences. Because force changes with rotor radius, the same RPM can produce very different g-force on different centrifuges.
This calculator helps you convert accurately so your spin conditions match protocol intent, regardless of rotor size.
Why converting RPM to g matters in real lab work
If a protocol says “spin at 12,000 ×g for 10 minutes,” setting 12,000 RPM instead can under-spin or over-spin your sample depending on rotor radius. That can affect pellet quality, phase separation, nucleic acid yield, and reproducibility.
- Reproducibility: Use the same effective force across instruments.
- Method transfer: Move protocols between microcentrifuges safely.
- Sample integrity: Avoid unnecessary over-centrifugation.
- Compliance: Match validated SOPs and published methods.
How to use this calculator correctly
Step 1: Enter rotor radius
Measure from the rotor center to the sample position. Enter the value and choose the correct unit (cm, mm, inches, or meters).
Step 2: Enter either g-force or RPM
Type the known value:
- Know ×g? Click Convert ×g to RPM.
- Know RPM? Click Convert RPM to ×g.
Step 3: Use the converted result
The calculator displays both values for quick cross-checking. You can copy the output directly into your run setup notes.
Worked examples
Example 1: Convert 10,000 ×g to RPM
With a rotor radius of 8 cm, 10,000 ×g corresponds to roughly 10,578 RPM.
Example 2: Convert 13,000 RPM to g-force
With a rotor radius of 7.5 cm, 13,000 RPM is about 14,171 ×g.
Common mistakes to avoid
- Using tube length as radius: Radius is center-to-sample, not total tube size.
- Mixing units: A mm/cm mismatch creates major errors.
- Confusing RCF and RPM in protocols: Always confirm which value is required.
- Ignoring rotor type changes: Fixed-angle vs swinging-bucket can alter effective conditions.
Quick reference: RPM vs RCF
- RPM = instrument speed setting.
- RCF (×g) = physical force on sample.
- Best practice: Report and compare centrifugation conditions in RCF where possible.
FAQ
Is RCF the same as g-force?
In centrifuge usage, yes. RCF is expressed as multiples of Earth gravity, commonly written as ×g.
Can two centrifuges use the same RPM for the same protocol?
Not reliably. Different rotor radii mean different RCF values at the same RPM.
What radius should I use?
Use the effective radius from the rotor center to the sample midpoint or pellet zone, according to your SOP or manufacturer guidance.
Why does this calculator ask for radius every time?
Because conversion depends directly on radius. Without it, RPM and g cannot be converted accurately.
Bottom line
A reliable g rpm converter calculator improves consistency, accuracy, and confidence in centrifuge protocols. Use RCF for method comparison, use RPM for instrument entry, and always include rotor radius in your calculations.