The formula
RCF (× g) = 1.118 × 10⁻⁵ × r × rpm²
rpm = √(RCF ÷ (1.118 × 10⁻⁵ × r))
r is the rotor radius in centimetres, measured from the centre of the rotor to the bottom of the tube. Use the maximum radius (rmax) from the rotor's spec sheet.
Worked example
13,000 rpm in a microcentrifuge with an 8.5 cm rotor gives about 16,060 × g.
Common questions
Why do protocols give × g instead of rpm?
The force depends on the radius as well as the speed, so the same rpm gives different forces in different rotors. × g transfers between centrifuges; rpm doesn't.
Can I go above the rpm this gives?
Check it is within your rotor's maximum rated speed, which varies with the rotor and the tubes or adaptors in it.
This calculator is checked against independent calculations before every release. How we check our calculators.