Centrifuge speed calculator
Turn a protocol's 1,000 × g at a 10 cm rotor radius into the rpm to set, using standard gravity of 9.80665 m/s². Enter the radius and the target RCF, and stop copying rpm between rotors of different sizes. Free in your browser.
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Worked example
- Radius
- 10
- Rcf
- 1,000
- Rpm
- 2,990.4167719726
Relative centrifugal force, often written RCF or × g, is the acceleration a sample feels in a spinning rotor expressed as a multiple of standard gravity. Protocols quote RCF because the same speed on two rotors with different radii produces different g-force. This centrifuge speed calculator inverts the laboratory identity: given a strictly positive rotor radius in centimetres and a strictly positive target RCF, it returns the rotational speed in revolutions per minute that produces that force at that radius.
What RCF, rotor radius, and RPM mean together
Relative centrifugal force, written RCF or times g, is the centripetal acceleration at a point in a spinning rotor divided by standard gravity. Standard gravity here is the conventional value 9.80665 metres per second squared, not a local survey of g at the bench.
Because acceleration equals omega squared times radius, two rotors that share a speed still deliver different RCF whenever their sample radii differ; that is why protocols quote a target RCF instead of a shared RPM, and why a centrifuge speed calculator needs both the rotor radius and the desired g-force. Angular speed omega equals two pi times revolutions per second, or two pi times RPM divided by sixty.
Substituting into RCF equals omega squared r over g and solving for RPM produces the closed form RPM equals thirty over pi times the square root of RCF times g over r, with r in metres. Send a strictly positive radius in centimetres and a strictly positive target RCF; the response is the instrument speed in revolutions per minute for that pair.
What you can do with it
Protocol transfer between rotors
Convert a protocol RCF into the RPM setting for a new rotor whose radius differs from the instrument that published the method.
Teaching labs and SOP keys
Generate deterministic RPM answers for RCF-and-radius drills, and reject non-positive radius or RCF instead of returning NaN.
FAQ
How do I convert RCF to centrifuge RPM?
Send a strictly positive rotor radius in centimetres and a strictly positive target RCF in ×g.
What units is the rotor radius in?
Divide a millimetre figure by ten before sending.
Why not copy the RPM from another centrifuge?
The same RPM on a different radius produces a different RCF. Protocols specify ×g so you recompute speed for the rotor you actually have.
What happens if radius or RCF is zero or negative?
Relative centrifugal force and rotor radius must both be strictly positive; failed validation is not billed.
Which radius from the rotor datasheet should I use?
The distance from the axis of rotation to the sample, often listed as the maximum or average radius on the rotor datasheet. Enter it in centimetres; a value in millimetres must be divided by ten first.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/phys/centrifuge-speed \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"radius":10,"rcf":1000}'const res = await fetch("https://api.kit.forhosting.com/phys/centrifuge-speed", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"radius": 10,
"rcf": 1000
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/phys/centrifuge-speed",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"radius": 10,
"rcf": 1000
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/phys/centrifuge-speed", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"radius":10,"rcf":1000}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"radius":10,"rcf":1000}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/phys/centrifuge-speed", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"radius": 10,
"rcf": 1000
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "phys.centrifuge_speed",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Invalid radius or RCF values fail with invalid_input and are not billed.
What RCF, rotor radius, and RPM mean together
Laboratory cards often print the centimetre approximation RCF equals 1.118 times ten to the minus five times radius in centimetres times RPM squared; this endpoint uses the exact SI rearrangement so the number matches textbook physics and the card to a few parts in ten thousand.
Input contract, units, errors, and the response shape
Numeric strings that parse to finite numbers are accepted so forms and notebooks can pass values without an extra cast. Convert millimetres from a datasheet by dividing by ten before sending, because the contract is centimetres to match the laboratory card. There is no rotor catalogue, no k-factor, no run-time or temperature model, and no unit conversion beyond centimetres to metres inside the square root. POST a JSON body with two required finite numbers: radius, the rotor radius in centimetres measured from the axis of rotation to the sample, often r_max or r_av from the rotor datasheet, and rcf, the target relative centrifugal force in multiples of g. Both radius and rcf must be strictly positive; zero, negative, missing, empty, NaN, and Infinity fail with invalid_input naming the field, and failed validation is not billed. Radius aliases r and radius_cm, and rcf aliases rcf_g, g_force, and relative_centrifugal_force, are accepted for real. On success the body echoes radius and rcf, returns rpm as the primary result rounded for stable goldens, and includes a formula string restating the SI identity with g equals 9.80665 plus a method label centrifuge_speed.
Where a centrifuge RPM calculator earns its keep
A ten-centimetre rotor at one thousand times g needs about two thousand nine hundred and ninety RPM; an eight-point-five-centimetre microcentrifuge rotor at sixteen thousand times g needs a much higher speed, and mixing those numbers by treating RPM as if it were RCF pellets a sample too hard or not at all. Teaching labs and exam keys need a deterministic oracle that rejects non-positive radius and RCF instead of returning NaN. Pin the rounded rpm in tests and you get reproducible speeds for standard operating procedures, notebooks, and edge workers without a chemistry library of your own. Molecular biology and clinical labs convert protocol RCF into an instrument setting whenever they change rotors or share a method across benchtops whose r_max differs. Instrument vendors and laboratory-information plugins can call a tiny parse API rather than reimplementing the square-root identity in every language.
Integration use cases
Instrument and notebook automation
Call a tiny parse API from LIS plugins, bench scripts, and CI fixtures instead of reimplementing the RCF-to-RPM square root in every language.
Technical questions
What does the centrifuge speed calculator cost?
The browser tool is free. API requests use prepaid KIT balance at $0.002 per successful call; invalid input is not billed.