Centrifuge RCF and RPM converter
Convert between relative centrifugal field and rotor speed, for a stated radius.
Nominal figures for the class, not a specification. Rotors within a class vary by roughly a tenth, and so does the field they produce — take the radii from your rotor’s manual where accuracy matters.
Axis to the bottom of the tube.
Axis to the top of the liquid. Optional.
Published protocols almost always mean the bottom of the tube, which is what rotor specifications quote.
Set the centrifuge to
Across the tube
Liquid top
5647× g
Average
8824× g
Tube bottom
12000× g
11236 rpm · 2.12× from top to bottom · k = 1510
The bottom of the tube sees 2.1× the force at the top of the liquid. A protocol quoting a single number almost always means the maximum, which is what a rotor's specification sheet gives.
Transfer a spin from another rotor
Matching × g between rotors does not reproduce a separation, because a longer tube gives a particle further to travel. The clearing factor accounts for that: run time scales with k.
Equivalent time on this rotor, at 11236 rpm
13.6min
k 2220 → 1510
The clearing factor describes an ideal particle sedimenting through water at 20 °C, all the way from the top of the liquid to the bottom of the tube. Viscous media, partly filled tubes and anything that pellets by aggregating rather than sedimenting will all depart from it, so treat the result as a starting point to check rather than a substitution.
RCF = ω²r ÷ g, ω = 2πN ÷ 60; k = ln(r_max/r_min) × 10¹³ ÷ (3600 ω²)- Sedimentation in a centrifugal field, and the clearing factor derived from it — Journal of the American Chemical Society, 1924
- Standard gravity, 9.80665 m/s², as fixed by the CGPM — 3rd General Conference on Weights and Measures, Resolution 2 (BIPM), 1901
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About this tool
Convert × g to rpm and back for your rotor, and see how far the field varies along the tube — the bottom commonly experiences twice the force of the top, which is why two labs following the same protocol can disagree. Also converts a run time between rotors using the clearing factor.
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Science last reviewed .