chemitrust.ai
Questions? Try ChemITrust AI Technical Help for FREE!
Centrifuge RPM to RCF Conversion (×g): Formula, Examples, and Calculator
Convert between RPM and RCF accurately for reproducible centrifugation results across different instruments.
Why RPM and RCF Are Not Interchangeable
Centrifuges are commonly set using RPM (revolutions per minute), but scientific protocols, kit inserts, and published methods specify RCF (relative centrifugal force, ×g). Because RCF depends on rotor radius, RPM values cannot be transferred directly between centrifuges.
This guide explains exactly how to convert RPM to RCF and RCF to RPM, step by step, and provides a lab-ready calculator built by ChemITrust AI to eliminate errors.
What Is the Difference Between RPM and RCF?
RPM
RPM describes how fast the rotor spins
RCF (×g)
RCF (×g) describes the actual acceleration applied to the sample
Two centrifuges running at the same RPM can generate very different g-forces if their rotor radii differ. For this reason, RCF is the only transferable parameter across instruments.
The RPM to RCF Conversion Formula
Convert RPM → RCF (×g)
\textbf{RCF (×g)} = 1.118 \times 10^{-5} \times r(\text{cm}) \times \text{RPM}^2
Where:
  • r (cm) = distance from rotor axis to the sample (in centimeters)
  • RPM = revolutions per minute
  • 1.118 × 10⁻⁵ is the standard conversion constant
Convert RCF (×g) → RPM
\textbf{RPM} = \sqrt{\dfrac{\text{RCF}}{1.118 \times 10^{-5} \times r(\text{cm})}}
This reverse formula allows you to determine the required RPM setting when your protocol specifies RCF and you know your rotor radius.
How to Choose the Correct Rotor Radius
The radius used in the calculation directly affects the result.
Most centrifuge manuals define:
rmax
distance to the bottom of the tube (recommended for pelleting)
ravg
distance to the center of the sample column
rmin
distance to the top of the liquid

✅ Best practice: For pellet formation (DNA, RNA, cells, protein precipitates), use rmax unless the protocol states otherwise.
⚠️ Unit warning: Always convert millimeters to centimeters (e.g., 85 mm = 8.5 cm).
Worked Examples
Example 1: Convert RPM to RCF
Given:
  • RPM = 13,000
  • Rotor radius = 8.0 cm
\text{RCF} = 1.118\times10^{-5} \times 8.0 \times (13{,}000)^2
Result: ≈ 15,100 ×g
Example 2: Convert RCF to RPM
Given:
  • RCF = 5,000 ×g
  • Rotor radius = 15.0 cm
\text{RPM} = \sqrt{\dfrac{5{,}000}{1.118\times10^{-5} \times 15.0}}
Result: ≈ 5,460 RPM
Common RPM ↔ RCF Conversion Mistakes
❌ Using RPM values from another centrifuge
❌ Forgetting to convert mm to cm
❌ Using the wrong rotor radius definition
❌ Assuming swing-bucket and fixed-angle rotors behave identically
Even small errors can result in incomplete pelleting, poor reproducibility, or sample loss.
Use the ChemITrust AI RPM ↔ RCF Calculator
Manual calculations are error-prone and time-consuming. ChemITrust AI provides a dedicated centrifuge RPM ↔ RCF calculator designed for real laboratory use.
Why use the ChemITrust AI calculator?
  • ✅ Supports both RPM → RCF and RCF → RPM
  • ✅ Radius-aware (cm-based, lab-correct math)
  • ✅ Prevents unit and formula mistakes
  • ✅ Ideal for method transfer and SOP writing
Ready to Convert?
Frequently Asked Questions
What does RCF mean in centrifugation?
RCF (relative centrifugal force) expresses centrifugal acceleration relative to gravity (×g) and accounts for rotor radius and speed.
Why is RCF better than RPM?
RCF allows results to be reproduced across different centrifuges and rotor designs, while RPM does not.
Does higher RPM always mean higher RCF?
Yes. RCF increases with the square of RPM, meaning small RPM increases can dramatically raise g-force.
Which radius should I use for pelleting?
Use the maximum radius (rmax) unless the protocol specifies otherwise.