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Practical Centrifuge

Centrifuge converter (rpm ↔ RCF ×g)

Convert between centrifuge speed (rpm) and relative centrifugal force (RCF, ×g) using rotor radius. Supports radius units (mm/cm/in), a quick reference table, and copy/export features.

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How to use (3 steps)

  1. Pick an example or choose a mode (rpm → ×g / ×g → rpm).
  2. Confirm the radius (distance from rotor center to sample) and unit (mm/cm/in).
  3. Enter rpm or ×g to see the converted result.

RCF depends on how radius is defined (rmax/ravg, etc.). Use the value provided in your rotor manual if possible.

Quick protocol workflow (when switching centrifuges)

  1. Convert the original protocol rpm to RCF (xg) using the original rotor radius.
  2. Keep that target RCF, then convert back to rpm with your destination rotor radius.
  3. Record both the radius definition and units (mm/cm/in) in your note so the run can be reproduced.

This keeps force level consistent across rotors better than copying rpm alone.

Input (radius, rpm/RCF)

What to solve for
Radius (important)

Distance from rotor center to the sample position. Use your rotor manual if possible.

Custom radius
RPM (speed)

Result (conversion)

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Formula used (coefficient 1.118×10^-5) 
RCF(×g) = 1.118×10^-5 × r(cm) × rpm^2
rpm = sqrt( RCF / (1.118×10^-5 × r(cm)) )
r(cm) = r(mm) / 10
r(cm) = r(inch) × 2.54
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How it’s calculated

This tool converts radius to cm and uses a commonly used formula.

RCF depends on how radius is defined (rmax/ravg, etc.). If results look off, recheck units (mm/cm/in) and your radius definition.

FAQ

What is RCF (×g)?
It is the relative centrifugal force expressed as a multiple of gravitational acceleration (g). Protocols often use ×g to compare conditions across different centrifuges and rotors.
Which radius should I use?
Use the distance from the rotor center to the sample position. Rotor manuals often list it as “radius”, “rmax”, or “ravg”. Use the manual value if possible.
Should I use rmax or ravg?
Follow your protocol definition. If unsure, rpm is fine when using the same rotor. When changing rotors, using the manual value (often ravg) is usually safer for conversions.
I want to reproduce an rpm protocol on a different centrifuge.
RCF changes with radius even at the same rpm. Convert the original rpm to ×g first, then convert ×g back to rpm using your rotor radius.
My result differs from other sites.
Differences can come from constants, the definition of g, and how radius is defined (cm/mm, rmax/ravg). This tool uses a common formula with radius in cm.
Can I enter 0 rpm or 0 ×g?
Yes. Entering 0 gives 0 as the result (radius must be non-zero).
It feels too strong/too weak.
Common causes are unit mistakes (mm vs cm) and radius definition differences. Recheck units and radius.