BioDeviceHub

RCF to RPM Centrifuge Calculator

Convert centrifuge speed in rpm to relative centrifugal force (× g), find the rpm for a target g-force, or the rotor radius that gives a force at a speed.

Formula

RCF=1.118×10−5  r  rpm2\mathrm{RCF} = 1.118\times 10^{-5}\;r\;\mathrm{rpm}^{2}
rpm=RCF1.118×10−5 r\mathrm{rpm} = \sqrt{\dfrac{\mathrm{RCF}}{1.118\times 10^{-5}\,r}}
r=RCF1.118×10−5 rpm2r = \dfrac{\mathrm{RCF}}{1.118\times 10^{-5}\,\mathrm{rpm}^{2}}
RCF\mathrm{RCF}
relative centrifugal force, as a multiple of standard gravity (× g)
rr
radius from the centre of rotation to the sample, in cm
rpm\text{rpm}
rotor speed, in revolutions per minute

How it works

The force on a sample in a centrifuge depends on how fast the rotor turns and on how far the sample is from the axis. Relative centrifugal force expresses that acceleration, r ω², as a multiple of standard gravity (9.80665 m/s²). Converting rpm to radians per second and the radius to metres gives the constant 1.118 × 10⁻⁵.

Because force rises with the square of the speed, the same rpm gives different forces in different rotors. Protocols written in × g transfer between centrifuges; protocols written in rpm do not.

Worked example

A rotor with a 10 cm radius spins at 3,000 rpm.

  1. RCF = 1.118 × 10⁻⁵ × 10 cm × 3,000² = 1.118 × 10⁻⁵ × 10 × 9,000,000.

The sample experiences about 1,006 × g.

These are the values the calculator opens with, so you can check its output against this example.

Assumptions

  • The radius is measured to the point of interest in the tube. The maximum radius, at the bottom of the tube, gives the highest force.
  • The rotor is at constant speed. Acceleration and braking are not included.

Common mistakes

  • Copying an rpm setting from a protocol written for a different rotor.
  • Entering the rotor diameter instead of the radius, which doubles the result.
  • Entering the radius in mm as if it were cm. The unit selector handles both.

Related tools

Centrifuge k-Factor and Pelleting Time Calculatork-factor, pelleting time, and run time between rotorsOpen calculatorHemocytometer Cell Counting CalculatorCells per mL from a hemocytometer countOpen calculatorCell Dilution CalculatorDilute a cell suspension to a target densityOpen calculatorMolarity CalculatorMass, concentration or volume for a molar solutionOpen calculator

Related equipment

Service documentation, failure modes and parts for the instruments this calculation is used with.