Science
Centrifuge RCF (x g) to RPM Conversion Formula & Rotor Scaling
Convert RPM and relative centrifugal force using a specified radius in centimeters. Keep the inverse result unrounded and distinguish a numerical conversion from a permitted instrument setting.
Radius and speed determine relative acceleration
At the same RPM, a larger radius gives a larger RCF. At 12 cm and 10,000 RPM, the conventional coefficient 1.118 × 10^-5 gives 13,416 ×g; at 7 cm it gives 7,826 ×g. RCF is an acceleration ratio, not a mass or an absolute force in newtons.
The coefficient is a rounded conversion factor derived from angular speed and standard gravity. It does not make a measured radius or instrument setting exact. Use the radius corresponding to the protocol’s RCF definition. Maximum RCF uses maximum radius; average and minimum RCF refer to different positions in the sample.
Manufacturer specifications, rotor/adaptor configuration, tube limits and the protocol govern permitted operation. The following calculation does not check them or guarantee equivalent separation performance between rotors.
Calculate RCF from RPM
B2 is radius in centimeters, B3 is nonnegative RPM. Zero speed returns zero RCF. Missing inputs and nonpositive radius are rejected.
=IF(OR(NOT(ISNUMBER(B2)),NOT(ISNUMBER(B3))),"Enter numeric inputs",IF(B2<=0,"Invalid rotor radius",IF(B3<0,"Use nonnegative speed or RCF",0.00001118*B2*B3^2)))Calculate RPM from a target RCF
B4 is the target acceleration ratio in ×g. E3 retains the unrounded result. ROUND(E3,0) is a presentation choice, not a validated instrument setting; available speed increments and the protocol determine what can be set.
The two calculations have independent inputs: changing B4 does not alter the measured-speed calculation in E2.
=IF(OR(NOT(ISNUMBER(B2)),NOT(ISNUMBER(B4))),"Enter numeric inputs",IF(B2<=0,"Invalid rotor radius",IF(B4<0,"Use nonnegative speed or RCF",SQRT(B4/(0.00001118*B2)))))Try the example
Use the original values or change them to test your understanding.