Centrifuge Speed Calculator
Convert centrifuge RPM to RCF (×g), find the RPM for a target ×g (e.g. a protocol that says “spin at 10,000×g”), or solve for the rotor radius you need. Pure client-side — no data leaves your device.
RPM → RCF reference
| RPM | RCF |
|---|
The formula
This is the standard relative-centrifugal-force equation: it comes from RCF = ω²r/g₀ with ω = 2π·RPM/60, evaluated with the radius in centimetres. The calculator also inverts it: RPM = √(RCF ÷ (1.118×10⁻⁵ × r)), and r = RCF ÷ (1.118×10⁻⁵ × RPM²).
Worked example: to reach 20,000 ×g at 15,000 RPM you need a rotor of at least 7.95 cm maximum radius. And the classic anchor — 10,000 RPM with a 10 cm rotor — gives exactly 11,180 ×g.
Important: r is the maximum rotor radius (r_max, measured to the tube bottom), the lab standard for reporting RCF. Never exceed your rotor's rated maximum speed — this calculator is a planning aid, not a substitute for the centrifuge manual.
Related
Need the force in newtons for any rotating object (not just lab rotors)? That tool computes general centrifugal force F = m·ω²·r. This page is the lab-specific RCF (×g) solver: RPM, rotor radius, and ×g only.
Frequently asked questions
What is RCF (relative centrifugal force)?
RCF — relative centrifugal force — is the effective force on a sample in a centrifuge, expressed as a multiple of Earth's gravity (×g). It depends only on the rotor radius and the spin speed: RCF = 1.118×10⁻⁵ × r(cm) × RPM². Reporting ×g instead of RPM makes protocols rotor-independent.
How do I convert RPM to RCF (×g)?
Enter your RPM and the rotor's maximum radius in the calculator above (RPM → RCF mode). Example: 10,000 RPM with a 10 cm rotor gives 11,180 ×g. The calculator shows the exact formula it used so you can check the math.
My protocol says spin at 10,000×g — what RPM do I set?
Switch to the RCF → RPM mode and enter the target ×g plus your rotor's maximum radius. For a 10 cm rotor, 10,000 ×g needs 9,458 RPM. Always round to a speed your centrifuge supports and stay below the rotor's rated maximum.
Should I use the maximum or the average rotor radius?
Use the maximum radius (r_max), measured to the bottom of the tube — that is the lab standard for reporting RCF, and it is what centrifuge manufacturers quote. Using the average radius understates the force the pellet actually experiences.
Can I enter the radius in mm or inches?
Yes — pick mm or inch in the unit dropdown and the calculator converts to cm internally. For reference, 100 mm = 10 cm, and 3.937 in = 10 cm.
What is the difference between this and a centrifugal force calculator?
A general centrifugal force calculator computes force in newtons for any rotating object (F = m·ω²·r). This tool is the lab-specific RCF solver: it works only with RPM, rotor radius, and ×g — the three variables centrifuge protocols actually use. See our Centrifugal Force Calculator for the general-physics version.
Where does the 1.118×10⁻⁵ constant come from?
It is not empirical — it falls out of RCF = ω²r/g₀ with ω = 2π·RPM/60. Working through the units with the radius in centimetres gives 1.11824×10⁻⁵, conventionally rounded to 1.118×10⁻⁵. Our oracle cross-checked this constant against the first-principles derivation and they agree to 0.02%.
Example: what ×g does a microcentrifuge reach at 13,200 RPM?
With a typical 7.1 cm max rotor radius, 13,200 RPM gives 13,831 ×g. Enter those numbers in the RPM → RCF mode to verify — the reference table below the calculator shows the same value in context.
What RCF does an ultracentrifuge produce?
Very large numbers: 100,000 RPM with a 7 cm rotor gives 782,600 ×g. This is why ultracentrifuge rotors are small — RCF grows with the square of the speed, so doubling RPM quadruples the ×g.
Is this calculator a substitute for my centrifuge manual?
No. It is a planning aid for converting between RPM, ×g, and rotor radius. Always confirm the rotor's maximum rated speed and the correct r_max from the manufacturer's manual before spinning — exceeding a rotor's rating can destroy the rotor.
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