Centrifuge Calculator

Related Calculators

RCF: Relative centrifugal force, shown here as multiples of Earth's gravity, or x g. It tells you how strongly the sample is being spun compared with normal gravity [3].

RPM: Revolutions per minute. This is how fast the rotor turns, but by itself it does not fully describe the force on the sample because radius also matters [3].

Rotor radius (selected unit): The distance from the center of rotation to the sample position used in the calculation.

Radius position: The sample location represented by the radius value, such as r_max for the farthest point, r_min for the nearest point, or r_avg for an average position. Rotor type and sample position matter in centrifugation setup [2].

Calculated result: The converted main output. It is RCF when you start with RPM, or RPM when you start with target RCF.

Angular speed: Rotational speed in radians per second, a physics unit based on the solved or entered RPM.

Mistake: Entering tube length or rotor diameter into Rotor radius (selected unit) instead of the distance from the center of rotation to the sample position.
Fix: Measure or look up the true center-to-sample distance, then confirm it in Radius used in formula .

Mistake: Choosing the wrong Radius unit , such as typing 10 but leaving the unit as mm when the value is really cm.
Fix: Match the number and unit together. A quick check is that Radius used in formula should equal 100 mm for 10 cm.

Mistake: Mixing up r_max , r_avg , and r_min in Radius position .
Fix: Use the same sample position named in your protocol or rotor manual, and read the Radius position note before using the result.

Mistake: Filling in both Speed (RPM) and Relative centrifugal force (x g) and assuming both are used at once.
Fix: Only the mode-specific input is used. In RCF from RPM mode, the calculator reads Speed (RPM) ; in RPM from RCF mode, it reads Relative centrifugal force (x g) .

Mistake: Forgetting that RPM rounding step can change the displayed speed when solving for RPM.
Fix: If your centrifuge accepts exact values, choose No rounding . If your machine uses increments, pick the closest practical step and compare the rounded result with the raw value note.

Mistake: Treating Calculated result as directly comparable across different rotors without checking radius.
Fix: Compare runs using Relative centrifugal force (x g) and the same radius basis, because the same RPM gives different force at different radii.

• The calculator uses the standard lab conversion between RCF, radius, and RPM. Real instruments can differ slightly because of calibration, acceleration, braking, and control tolerances.
• You must supply the correct sample radius. Using the wrong Radius position can materially change the result, especially with long tubes or swing-out rotors.
• This page treats the entered radius as a single known value. It does not calculate r_avg from separate minimum and maximum radii.
• Results are only valid for positive, finite inputs. Rotor radius (selected unit), Speed (RPM), and Relative centrifugal force (x g) must be greater than 0 when required.
• If you choose an RPM rounding step, the rounded RPM may not produce the exact target RCF. It is a practical machine-setting estimate.
• Display format changes how numbers look, not the underlying math.

Core equations

The calculator converts the entered radius to millimeters, then uses the standard centrifuge convenience form for radius in mm.

RCF = 1.118e-6 * r_mm * RPM^2

RPM = sqrt(RCF / (1.118e-6 * r_mm))

ω (angular speed in rad/s) = 2 * pi * RPM / 60

The constant 1.118e-6 is the common RCF conversion factor for radius in millimeters, and RCF is expressed as a multiple of gravity [3].

Unit conversion

The calculator first converts the selected radius to millimeters so one equation form can be used consistently.

r_mm = r_cm * 10

r_mm = r_in * 25.4

r_mm = r_mm

Radius position handling

Radius position does not change the number by itself. It changes the meaning of the entered radius so you can match a protocol or rotor manual. This matters because rotor type and sample position are part of choosing centrifugation conditions [2].

If your manual gives one stated radius, use Single stated radius. If it specifies r_max, r_avg, or r_min, enter that exact value and choose the matching position.

Rounding and display

When solving for RPM, the raw RPM is calculated first. If an RPM rounding step is selected, the displayed main RPM can be rounded to the nearest 1, 10, 50, or 100 rpm for easier use on real instruments.

Display format only changes number presentation. It does not change the calculated physics values.

Worked mini-example

Example:

radius = 100 mm and speed = 5000 RPM.

RCF = 1.118e-6 * 100 * 5000^2

RCF = 2795 x g

ω = 2 * pi * 5000 / 60 = 523.6 rad/s

This means the sample feels about 2795 times Earth's gravity at that radius.

Practical interpretation

At a fixed radius, increasing RPM raises RCF very quickly because RPM is squared. At a fixed RCF target, a larger radius means you need less RPM to reach the same force.

Assumptions used

This calculator assumes steady rotation, a correctly measured radius, and the standard RCF relationship used in lab centrifugation. Results can differ from instrument readouts if a manufacturer defines the operating radius differently or if the rotor geometry is not matched to the chosen radius position [2][3].