Centrifuge RCF to RPM Calculator (g-Force)
Relative centrifugal force in × g for a given rotor speed and radius, and the rpm needed to reach a protocol's g-force on your rotor.
Results
The dashed line marks the value you entered.
What this tool does
Protocols give the force in × g because it is what the sample feels, while a centrifuge dial shows rpm, and the same rpm gives a different force in every rotor: RCF grows with the square of the speed and in proportion to the radius. That is why 'spin at 10 000 rpm' means little without the rotor, and why swapping a small rotor for a large one can over-spin a pellet. Use the radius to the sample, which is often given for the bottom of the tube; the maximum radius is printed on the rotor or in its manual.
Formula
RCF = ω² r ÷ g = 1.118 × 10⁻⁵ × r(cm) × rpm² · rpm = √(RCF ÷ (1.118 × 10⁻⁵ r))
Variables
| Symbol | Meaning | Unit |
|---|---|---|
rp | Rotor speed | rpm |
rc | Radius from the axis to the sample | cm |
gt | Force you want | × g |
RCF | Relative centrifugal force (RCF) | × g |
RP | Speed needed for that force | rpm |
AC | Acceleration at the sample | m/s² |
OM | Angular speed | rad/s |
VT | Speed of the sample around the circle | m/s |
Worked example
- Rotor speed4000 rpm
- Radius from the axis to the sample8.4 cm
- Force you want5000 × g
- Relative centrifugal force (RCF)1503 × g
- Speed needed for that force7296 rpm
- Acceleration at the sample14,739 m/s²
- Angular speed418.9 rad/s
- Speed of the sample around the circle35.2 m/s
Limitations
- Mixing units is the most common source of error. Convert every input to the units shown next to each field before calculating.
- The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.