Centrifuge RCF to RPM Calculator
Converting between RPM (rotor speed) and RCF (g-force) is essential for following centrifugation protocols correctly. A protocol that specifies 500 x g requires different RPM settings depending on the rotor radius. This calculator converts in both directions: enter RPM and radius to get RCF, or enter RCF and radius to get RPM. The formula used is the standard industry equation RCF = 1.118 x 10^-5 x r x N^2, where r is the rotor radius in millimetres and N is RPM.
RCF and RPM conversion formulas
RCF = 1.118 x 10^-5 * r * N^2
N = sqrt(RCF / (1.118 x 10^-5 * r))
Where RCF is the relative centrifugal force (x g), r is the rotor radius in millimetres, and N is the speed in revolutions per minute. The constant 1.118 x 10^-5 converts the result into multiples of g (9.81 m/s2). This formula is standard across major centrifuge manufacturers including Beckman Coulter, Eppendorf, and Thermo Fisher Scientific.
Common centrifugation conditions
- Mammalian cell pelleting: 200 to 500 x g, 5 to 10 minutes at 4 degrees Celsius
- Bacteria: 3,000 to 5,000 x g, 10 to 15 minutes
- Platelet-rich plasma preparation: 200 x g for 10 minutes
- Mitochondria: 10,000 x g for 10 minutes
- Microsome/ribosome isolation: 100,000 x g for 60 minutes (ultracentrifuge required)
Centrifuge RCF and RPM: frequently asked questions
What is RCF (relative centrifugal force)?
RCF (relative centrifugal force), also called g-force, is the ratio of the centrifugal acceleration to the standard acceleration due to gravity (9.81 m/s2). An RCF of 1000 x g means the centrifugal force is 1,000 times the force of gravity.
What is the formula to convert RPM to RCF?
RCF = 1.118 x 10^-5 x r x N^2, where r is the rotor radius in millimetres (from the centre of rotation to the sample), and N is the speed in revolutions per minute. This is the standard formula published by most centrifuge manufacturers and referenced by NIST.
What is the rotor radius I should use?
Use the maximum radius (r max) from the rotor centre to the bottom of the sample tube for the highest g-force, or the average radius to the middle of the sample tube for mean g-force. The rotor specification sheet or manufacturer's manual lists these values.
Why do protocols specify RCF instead of RPM?
RCF is independent of rotor design. Two centrifuges running at the same RPM but with different rotor radii produce different g-forces. Specifying RCF ensures the same centrifugal force regardless of which centrifuge or rotor is used.
What RCF is needed to pellet bacteria vs mammalian cells?
Mammalian cells typically pellet at 200 to 500 x g for 5 to 10 minutes. Bacteria require 3,000 to 5,000 x g for 10 to 15 minutes. Mitochondria pellet at approximately 10,000 x g and microsomes/ribosomes require ultracentrifugation above 100,000 x g.
Official sources
- Beckman Coulter centrifuge physics documentation: Beckman Coulter Centrifugation Fundamentals.
- Thermo Fisher Scientific centrifuge selection guide: Thermo Fisher Centrifuge Guide.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.