Centrifuge Calculator

General Physics

Calculate Relative Centrifugal Force (RCF), RPM, or radius for your centrifuge setup. Select the value you want to find and enter the other two parameters.

Practical Examples

See how the Centrifuge Calculator is used in common laboratory scenarios.

Calculating RCF for Cell Pelleting

rcf

A common protocol requires pelleting cells at a specific g-force. Given the RPM and radius, find the RCF.

Type: rcf

Radius: 100 mm

RPM: 2500

Determining RPM for a DNA Precipitation Protocol

rpm

A protocol specifies an RCF of 12,000 x g. Your centrifuge has a rotor radius of 85 mm. What RPM should you set?

Type: rpm

Radius: 85 mm

RCF: 12000 g

Finding the Required Rotor Radius

radius

You need to achieve an RCF of 500 x g at 1500 RPM. What is the minimum rotor radius required?

Type: radius

RPM: 1500

RCF: 500 g

High-Speed Protein Separation

rcf

An ultracentrifuge runs at 50,000 RPM with a 50 mm rotor. Calculate the immense g-force generated.

Type: rcf

Radius: 50 mm

RPM: 50000

Other Titles
Understanding the Centrifuge Calculator: A Comprehensive Guide
Dive deep into the principles of centrifugal force, its calculation, and practical applications in scientific research.

What is a Centrifuge and Relative Centrifugal Force (RCF)?

  • The Role of a Centrifuge in the Lab
  • Defining Relative Centrifugal Force (RCF)
  • Why We Use RCF Instead of RPM
A centrifuge is a laboratory device that uses centrifugal force to separate particles from a solution according to their size, shape, density, viscosity of the medium, and rotor speed. By spinning samples at high speeds, it generates a force that pushes denser components to the bottom of the tube, a process known as pelleting. This is fundamental in biology, chemistry, and medicine for isolating cells, organelles, proteins, and nucleic acids.
Defining Relative Centrifugal Force (RCF)
Relative Centrifugal Force (RCF), also known as g-force, is the force exerted on the contents of the rotor, measured in multiples of Earth's gravitational force (g). It is the standard and most accurate way to quantify the force applied during centrifugation because it is independent of the centrifuge model.
Using RCF ensures that separation protocols are reproducible across different centrifuges and rotors. A protocol that specifies an RCF of 1000 x g will produce the same separation effect regardless of the specific equipment used, as long as the RCF is correctly calculated.

Key Concepts

  • Centrifugal force pushes denser particles outward.
  • RCF is a standardized measure of this force, expressed in multiples of gravity (g).
  • Scientific protocols specify RCF (g-force) for reproducibility, not RPM.

Step-by-Step Guide to Using the Centrifuge Calculator

  • Selecting the Calculation Type
  • Entering Input Values
  • Interpreting the Results
Our calculator simplifies the conversion between RCF, RPM, and radius. Follow these steps for an accurate calculation.
1. Select the Calculation Type
Begin by choosing which value you want to calculate from the 'Calculation Type' dropdown menu. You can choose to solve for RCF, RPM, or Radius.
2. Enter Input Values
Based on your selection, two of the three input fields will be active. Enter the known values: Radius (in millimeters), Speed (in RPM), or RCF (in g-force). It is crucial to measure the radius from the center of the rotor to the bottom of the sample tube for accuracy.
3. Interpret the Results
After clicking 'Calculate,' the tool will display the result in the corresponding unit. This value can be directly used to set up your centrifuge or to document your experimental parameters.

Example Scenario

  • You want to find the RPM needed to achieve 10,000 x g with a 95 mm rotor.
  • Select 'Calculate RPM' as the calculation type.
  • Enter '95' for Radius and '10000' for RCF.
  • The calculator provides the precise RPM setting you need to use.

Mathematical Derivation and Formulas

  • The Core RCF Formula
  • Solving for RPM
  • Solving for Radius
The Core RCF Formula
The relationship between RCF, RPM, and radius is defined by a standard formula. The force is proportional to the radius and the square of the angular velocity. The formula is: RCF = 1.118 x 10⁻⁵ r (RPM)²
Where: RCF is the relative centrifugal force in g-force, 'r' is the radius in centimeters, and RPM is the speed in revolutions per minute. Our calculator handles the conversion from millimeters to centimeters internally.
Derived Formulas
By rearranging the core formula, we can solve for RPM or radius: RPM = √[RCF / (1.118 x 10⁻⁵ r)] and r (cm) = RCF / (1.118 x 10⁻⁵ (RPM)²)

Calculation Insight

  • Doubling the RPM quadruples the RCF.
  • Doubling the radius doubles the RCF.
  • The constant 1.118 x 10⁻⁵ standardizes the units to g-force, cm, and RPM.

Real-World Applications of Centrifugation

  • Biology and Medicine
  • Chemistry and Materials Science
  • Food and Beverage Industry
Centrifugation is a workhorse technique used across numerous scientific and industrial fields.
Biology and Medicine
In clinical labs, centrifuges separate blood components, such as plasma and red blood cells. In research, they are used to pellet cells, isolate subcellular organelles like mitochondria and nuclei, and precipitate DNA and proteins.
Chemistry
Chemists use centrifuges to separate precipitates from reaction mixtures, analyze polymers, and in the purification of chemical compounds. Isotope separation, such as enriching uranium for nuclear applications, relies on specialized gas centrifuges.
Food Industry
Centrifuges are used to clarify juices and wines, separate cream from milk (for butter and cheese), and process oils. They ensure product quality and consistency.

Application Examples

  • Separating plasma from blood for diagnostic testing.
  • Isolating mitochondria from cells to study cellular respiration.
  • Clarifying wine by removing yeast and other particulates.

Common Misconceptions and Best Practices

  • RPM vs. RCF: The Critical Difference
  • Accurate Radius Measurement
  • Balancing the Rotor
Avoiding common mistakes is essential for safe and reproducible centrifugation.
RPM vs. RCF
The most common misconception is treating RPM and RCF as interchangeable. Different rotors have different radii, so the same RPM will produce different g-forces. Always follow protocols based on RCF (g-force) for reliable results.
Accurate Radius Measurement
An incorrect radius is a frequent source of error. For swinging-bucket rotors, measure to the bottom of the tube when it is horizontal. For fixed-angle rotors, measure to the middle of the tube. Refer to the manufacturer's manual for the most accurate radius (rmax and rmin).
Balancing the Rotor
Always balance centrifuge tubes with a tube of the same type, size, and weight placed opposite. An unbalanced rotor can cause dangerous vibrations, damage the centrifuge, and ruin your samples.

Safety and Accuracy Tips

  • Never use RPM from one centrifuge for another without converting to RCF first.
  • Always measure the radius carefully or use the value from the rotor manual.
  • Ensure the rotor is properly balanced before every run.