Example Data Table
| Rotor Radius |
RPM |
Calculated Force |
Common Use |
| 8 cm |
3000 |
805 × g |
Gentle clarification |
| 10 cm |
5000 |
2795 × g |
Routine pellet step |
| 12 cm |
10000 |
13416 × g |
High force separation |
| 15 cm |
12000 |
24149 × g |
Dense sample spin |
Formula Used
The calculator uses the standard relative centrifugal force equation:
RCF = 1.118 × 10-5 × r × RPM2
Here, RCF is force in multiples of gravity. The value r is the effective rotor radius in centimeters. RPM is revolutions per minute.
To find RPM, the formula becomes:
RPM = √(RCF ÷ (1.118 × 10-5 × r))
To find radius, the formula becomes:
r = RCF ÷ (1.118 × 10-5 × RPM2)
The page also calculates acceleration, angular velocity, and g-minutes when enough data is supplied.
How to Use This Calculator
- Select the calculation mode.
- Enter the effective radius, or enter rotor diameter.
- Add RPM or target force as required.
- Enter run time when g-minute exposure is needed.
- Add sample and protocol notes for better records.
- Press the calculate button.
- Review the result above the form.
- Use CSV or PDF export for records.
Understanding Centrifuge G Force
Centrifuge force is often called relative centrifugal force. It tells how many times stronger the spin is than normal gravity. This value is more useful than speed alone. Two rotors can share the same speed and still create different force. Radius changes the result, so the calculator asks for the working radius.
Why Radius Matters
The effective radius is the distance from the rotor center to the sample position. A larger radius creates higher force at the same speed. This is why protocols should mention RCF when possible. RCF helps another lab repeat the same separation with a different centrifuge. The calculator also accepts rotor diameter, then estimates radius from half the diameter.
Practical Lab Planning
Many protocols list speed in RPM. Others list target force in g. This page supports both directions. You can find force from speed, find speed from force, or find radius from force and speed. Extra outputs include angular velocity, acceleration, and g minutes. These values help compare gentle spins, pellet recovery, washing steps, and clarification runs.
Safe Use
Always check the rotor manual before setting a run. Never exceed the rated speed, tube limit, or load rule. Balance opposite buckets carefully. Use sealed tubes when samples may leak. Treat calculated results as planning values. Actual performance can vary with adapter depth, tube shape, fill level, and rotor design.
Result Interpretation
Small changes in speed can create large force changes. That happens because speed is squared in the formula. Doubling RPM gives about four times the force, when radius stays the same. A small radius error can also matter during sensitive work. Measure to the sample bottom for pellets. Measure to the liquid midpoint for mixed samples.
Record Keeping
The export buttons make reporting easier. CSV files are useful for spreadsheets. PDF summaries are useful for lab notebooks, validation packets, and quality records. Keep the sample name, protocol note, and date with each result. This makes later review faster and reduces mistakes during repeated work. When sharing a method, include unit choices and rounding notes. State whether the radius came from a rotor chart or direct measurement. Clear details help technicians reproduce settings without guessing later during busy sample preparation days.
FAQs
What does centrifuge g force mean?
It means relative centrifugal force. It shows how many times stronger the spin is than normal gravity. A value of 1000 × g means the sample experiences one thousand times gravity.
Is RPM the same as g force?
No. RPM is speed. G force depends on both speed and rotor radius. The same RPM can produce different force in different rotors.
Which radius should I enter?
Use the effective radius from the rotor center to the sample position. For pelleting, use the distance to the sample bottom when possible.
Can I use rotor diameter instead?
Yes. Enter the rotor diameter if radius is unknown. The calculator estimates radius as half the diameter. Direct radius is better when available.
Why does a small RPM change matter?
Speed is squared in the formula. This means force rises quickly when RPM increases. Doubling speed gives about four times the force.
What are g-minutes?
G-minutes estimate exposure by multiplying force by run time. They help compare spin steps, but they do not replace a validated protocol.
Can this calculator replace the rotor manual?
No. Always follow the rotor manual, tube limits, and safety instructions. The calculator is for planning and conversion only.
Why export results?
Exports help keep clear records. CSV files work well in spreadsheets. PDF files are useful for lab notebooks, reviews, and validation records.