Centrifuge Calculator
Last Updated: October 29, 2025
Calculate centrifuge RCF (relative centrifugal force), RPM, radius, and separation parameters using centrifuge equations. Essential tool for laboratory centrifuges, material separation, and processing applications.
Calculator
Enter your values below to calculate centrifuge parameters instantly.
Choose your calculation method and enter the required values for accurate centrifuge calculations.
Rotation speed in revolutions per minute
Distance from rotation axis to sample (typically in cm for lab centrifuges)
Results
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Table of Contents
What is Centrifuge Calculator?
Understanding Centrifuge Operation and Relative Centrifugal Force
The Centrifuge Calculator is a specialized tool that calculates relative centrifugal force (RCF), rotation speed (RPM), radius, and separation parameters for laboratory and industrial centrifuges. Centrifuges use rotational motion to separate materials by density through the application of centrifugal force, with RCF representing multiples of Earth's gravity.
This calculator is essential for laboratory operations, medical diagnostics, industrial processing, and research applications. It provides accurate calculations for centrifuge operations using multiple methods, including RCF from RPM and radius, RPM from RCF, radius calculations, and separation time estimates based on particle characteristics.
Key Concepts
Relative Centrifugal Force (RCF): Force expressed as multiples of gravity (× g). Also called "g-force" or "g-value". RCF of 1000×g means the force is 1000 times Earth's gravity. This standardized measure allows comparison across different centrifuge designs regardless of rotor size.
RPM: Revolutions per minute - rotation speed. The number of complete rotations the centrifuge makes per minute. Higher RPM generates higher RCF for a given radius. Typical laboratory centrifuges operate from 1,000 to 100,000+ RPM.
Radius (r): Distance from rotation axis to sample, typically measured in centimeters (cm). The effective radius depends on where the sample is placed in the rotor. Larger radii produce higher RCF at the same RPM.
Separation Time: Time required for particle separation, measured in minutes or hours. Depends on particle size, density difference, medium viscosity, and RCF. Higher RCF reduces separation time.
Particle Size: Diameter of particles to be separated, measured in micrometers (μm) or nanometers (nm). Smaller particles require higher RCF or longer times for separation. Ultracentrifuges can separate particles as small as viruses (20-300 nm).
Density Difference: Difference in density between particles and the surrounding medium, typically in g/cm³. Larger density differences enable faster separation. Density gradient centrifugation uses density differences for separation.
Physical Interpretation
Centrifuges accelerate particles outward by spinning samples at high speeds. The centrifugal force pushes denser particles toward the bottom (or outward in horizontal rotors), while less dense materials remain closer to the top (or center). This creates separation based on density, size, and shape. RCF is more useful than RPM alone because it accounts for the rotor radius - two centrifuges at the same RPM but different radii will produce different separation forces.
The relationship RCF = 1.118 × 10⁻⁵ × r × rpm² shows that RCF increases with the square of RPM - doubling the speed quadruples the force. It also increases linearly with radius. This means samples placed at the outer edge of a rotor experience much higher forces than those near the center, which is why proper sample placement is critical for consistent results.
Types of Centrifuges
Different centrifuge types operate at different speed ranges: low-speed centrifuges (up to 6,000 RPM), high-speed centrifuges (6,000-30,000 RPM), and ultracentrifuges (30,000-100,000+ RPM). Ultracentrifuges can generate forces exceeding 1,000,000×g, enabling separation of macromolecules, viruses, and subcellular components. The choice of centrifuge depends on the application and required RCF.
Historical Development
Centrifuges were developed in the late 19th century for separating biological materials, particularly milk and blood components. The relationship between RCF, RPM, and radius (RCF = 1.118 × 10⁻⁵ × r × rpm²) allows precise control of separation forces. Modern centrifuges operate at speeds from hundreds to hundreds of thousands of RPM, creating forces thousands to millions of times gravity. Ultracentrifuges developed in the 1920s enabled separation of subcellular components, leading to Nobel Prize-winning discoveries in biochemistry and molecular biology.
Units and Conversions
RCF Unit: × g (multiples of gravity) - dimensionless ratio
RPM Unit: revolutions per minute (min⁻¹ or rpm)
Radius Unit: typically centimeters (cm) in laboratory applications
Conversion: RCF = 1.118 × 10⁻⁵ × r(cm) × rpm²
Common RCF Values: 100-500×g (low-speed), 1,000-15,000×g (high-speed), 20,000-100,000+×g (ultracentrifuge)
Formulas and Equations
Centrifuge Calculation Methods
1. Calculate RCF from RPM and Radius
RCF = (1.118 × 10⁻⁵) × r × rpm²
Where:
- • RCF = Relative Centrifugal Force (× g)
- • r = Radius from axis to sample (cm)
- • rpm = Revolutions per minute
- • 1.118 × 10⁻⁵ = Conversion constant
Use case: Calculate RCF when you know rotation speed and sample radius. This is the standard method for converting between RPM and RCF in laboratory centrifuges. Essential for protocol standardization - many procedures specify RCF rather than RPM because RCF accounts for rotor size differences. Used when you need to replicate centrifugation conditions across different centrifuge models or rotor sizes.
2. Calculate RPM from RCF and Radius
rpm = √(RCF / (1.118 × 10⁻⁵ × r))
Where:
- • rpm = Revolutions per minute
- • RCF = Relative Centrifugal Force (× g)
- • r = Radius from axis to sample (cm)
Use case: Calculate required RPM when you know desired RCF and sample position. This is useful when protocols specify RCF rather than RPM. Essential when adapting protocols from scientific literature or when using a different centrifuge model. Derived by rearranging the RCF formula. The square root relationship shows that doubling RCF requires only √2 (1.41) times the RPM.
3. Calculate Radius from RCF and RPM
r = RCF / (1.118 × 10⁻⁵ × rpm²)
Where:
- • r = Radius from axis to sample (cm)
- • RCF = Relative Centrifugal Force (× g)
- • rpm = Revolutions per minute
Use case: Calculate optimal sample position (radius) when you know desired RCF and rotation speed. Helps determine where to place samples in the centrifuge rotor to achieve specific separation forces. Useful for optimizing protocols or when using fixed-angle rotors where radius varies with tube position. Derived by rearranging the RCF formula.
4. Calculate Separation Time
t = (18η × ln(r₂/r₁)) / (d² × Δρ × ω² × r_avg²)
Where:
- • t = Separation time (s)
- • η = Viscosity of medium (Pa⋅s)
- • d = Particle diameter (m)
- • Δρ = Density difference (kg/m³)
- • ω = Angular velocity (rad/s)
- • r_avg = Average radius (m)
Use case: Estimate separation time based on particle characteristics, medium properties, and centrifuge conditions. This formula (Stokes' law applied to centrifugation) shows that separation time decreases with larger particles, greater density differences, higher RCF, and lower viscosity. Simplified models provide approximations for practical use. More complex models account for particle shape, size distribution, and concentration effects. Critical for protocol development and optimization.
Applications of Centrifuges
Real-World Uses Across Industries
| Industry | Applications | Importance |
|---|---|---|
| Medical & Laboratory | Blood component separation, cell culture, DNA/RNA extraction, protein purification, sample processing | Critical for diagnostic procedures and research |
| Biotechnology | Protein isolation, cell separation, virus purification, vaccine production, bioreactor processing | Essential for bioprocessing workflows |
| Industrial Processing | Wastewater treatment, oil processing, chemical separation, material purification, food processing | Vital for large-scale separation processes |
| Pharmaceutical | Drug formulation, active ingredient separation, quality control, particle size analysis | Key for drug manufacturing and quality assurance |
| Research & Development | Material science, nanotechnology, particle analysis, density gradient separation | Fundamental for scientific research |
Examples of Centrifuge Calculations
Real-World Laboratory Applications
Example 1: Blood Separation Centrifuge
Given:
- • RPM: 3000 rpm
- • Radius: r = 10 cm
Step-by-step calculation:
Step 1: Apply RCF formula
RCF = (1.118 × 10⁻⁵) × r × rpm²
RCF = (1.118 × 10⁻⁵) × 10 × (3000)²
RCF = (1.118 × 10⁻⁵) × 10 × 9,000,000
RCF = 1,006.2 × g
Final Answer
1,006.2 × g
The centrifuge generates approximately 1006 times Earth's gravity, effectively separating blood components by density
Example 2: Required RPM for Specific RCF
Given:
- • Required RCF: 5000 × g
- • Radius: r = 15 cm
Step-by-step calculation:
Step 1: Apply RPM formula
rpm = √(RCF / (1.118 × 10⁻⁵ × r))
rpm = √(5000 / (1.118 × 10⁻⁵ × 15))
rpm = √(5000 / (1.677 × 10⁻⁴))
rpm = √29,821,000
rpm ≈ 5,461 rpm
Final Answer
5,461 rpm
To achieve 5000 × g RCF at a radius of 15 cm, the centrifuge must rotate at approximately 5,461 revolutions per minute
Example 3: Ultracentrifuge for Virus Separation
Given:
- • Required RCF: 100,000 × g
- • Rotor radius: r = 8 cm
- • Application: Separating virus particles (50-200 nm)
Step-by-step calculation:
Step 1: Calculate required RPM
rpm = √(RCF / (1.118 × 10⁻⁵ × r))
rpm = √(100,000 / (1.118 × 10⁻⁵ × 8))
rpm = √(100,000 / (8.944 × 10⁻⁵))
rpm = √1,118,032,787
rpm ≈ 33,442 rpm
Step 2: Convert to rotations per second
rps = 33,442 / 60 = 557.4 rotations per second
Step 3: Calculate angular velocity
ω = 2π × rps = 2π × 557.4 = 3,500 rad/s
Final Answer
33,442 rpm (3,500 rad/s)
Ultracentrifuge operation at over 33,000 RPM generates 100,000×g, enabling separation of nanometer-sized particles like viruses and subcellular components. This extreme force is necessary because small particles experience strong Brownian motion that opposes sedimentation.