Frequency to wavelength calculator
A 100 MHz radio carrier has a wavelength of about 3 metres in a vacuum: enter a frequency in hertz or a wavelength in metres and get the other, worked out from the exact speed of light, with the period and every step shown. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Radio frequency in hertz
- 100,000,000
- F
- 100,000,000
- Wavelength
- 2.99792458
- Lambda
- 2.99792458
- C
- 299,792,458
A frequency to wavelength calculator turns a radio frequency in hertz into the free-space wavelength in metres, and the reverse conversion from wavelength back into frequency, using the exact vacuum speed of light. Enter either frequency or free-space wavelength—never both—and the tool returns λ equals c over f or f equals c over λ, the shared period, substitution steps, and a clear direction label so you know which way the arithmetic ran. Antenna spacing, band planning, EM homework, and RF firmware tests all need the same deterministic pair without opening a spreadsheet or a full-wave simulator.
What free-space wavelength means for radio frequency
In free space an electromagnetic wave travels at the exact SI vacuum speed of light c equals two hundred ninety-nine million seven hundred ninety-two thousand four hundred fifty-eight metres per second. The free-space wavelength is the spatial period of that wave: lambda equals c divided by frequency f when f is in hertz and lambda is in metres. The inverse relation is equally fundamental: frequency equals c divided by lambda.
Those two identities are the backbone of radio, microwave, and millimeter-wave engineering whenever you need a first-order length scale before dielectric loading, ground planes, or waveguides enter the picture. A one-hundred-megahertz carrier has a free-space wavelength of about three metres; a two-point-four-gigahertz Wi-Fi channel sits near twelve and a half centimetres; a thirty-gigahertz mmWave tone compresses toward one centimetre.
The check path recomputes c over the provided value with the same fixed twelve-decimal rounding used for published fields, so a successful response always ships with steps you can assert in tests or worksheets. This landing is for free-space conversion only—not guided wavelength in waveguide, not optical refractive index paths, and not Doppler-shifted observed frequency.
Practical tips, limits, and related searches
Keep inputs inside the published absolute range so c divided by f or c divided by lambda cannot overflow into a non-finite result that the solver must reject. Convert megahertz or gigahertz to hertz before you call—one hundred megahertz is one times ten to the eight hertz—and convert centimetres or millimetres to metres the same way. Round-trip checks are easy: take a successful frequency-to-wavelength result, feed the published wavelength back into a second call, and confirm frequency matches within the same twelve-decimal rounding.
This landing targets people searching for a frequency to wavelength calculator, free-space RF lambda, or radio wave c over f online; it is not an LC resonant frequency tool, not a diffraction-grating angle solver, not a Doppler shift calculator, and not a waveguide cutoff finder. Prefer this capability when you already have either f or free-space lambda in SI units and only need the paired quantity plus period; if your source is a band plan table with mixed units, normalize first.
What you can do with it
Antenna half-wave element sizing
RF designers convert a target carrier frequency to free-space wavelength, then take a half-wave or quarter-wave fraction for initial dipole or monopole length before tuning.
FAQ
What formula converts frequency to free-space wavelength?
The inverse is f = c / λ.
What happens if frequency or wavelength is zero?
Division by zero is not a valid free-space wavelength or frequency.
Does this include waveguide or dielectric wavelength?
No. It is free-space only (vacuum speed of light). Guided wavelength, refractive index, and material loading are out of scope.
Is the frequency to wavelength calculator free?
The browser tool is free and runs locally.
Can I type megahertz or gigahertz directly?
No. Enter plain hertz and plain metres, so 100 MHz goes in as 100,000,000 Hz, and centimetres or millimetres need converting to metres first. Keeping base units avoids a result that is off by a factor of a thousand or more.
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/elec/wavelength-frequency-rf \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"frequency":100000000,"f":-1000000000000}'const res = await fetch("https://api.kit.forhosting.com/elec/wavelength-frequency-rf", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"frequency": 100000000,
"f": -1000000000000
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/elec/wavelength-frequency-rf",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"frequency": 100000000,
"f": -1000000000000
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/elec/wavelength-frequency-rf", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"frequency":100000000,"f":-1000000000000}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"frequency":100000000,"f":-1000000000000}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/elec/wavelength-frequency-rf", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"frequency": 100000000,
"f": -1000000000000
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "elec.wavelength_frequency_rf",
"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.
Limits
max_abs | 1000000000000 |
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
Zero or near-zero inputs are rejected with invalid_input because division by zero is not a physical free-space mode.
How to call the API and what comes back
Prefer numbers rather than pre-formatted engineering strings when you control the client; string numbers are accepted only when they match a strict finite numeric pattern. Send a JSON body with exactly one of two optional-but-required-as-a-pair fields: frequency in hertz (aliases f, freq, hz, frequency_hz) or wavelength in metres (aliases lambda, λ, wl, wavelength_m). Absolute values must stay within the published limit of one trillion so intermediate ratios remain finite in IEEE double precision on the Worker and in the browser. Both fields blank, both fields filled, non-finite numbers, values outside absolute limits, negative inputs, and zero or near-zero inputs all return invalid_input and are never charged. On success the response echoes rounded frequency and wavelength (with short aliases f and lambda), sets c and speed_of_light to two hundred ninety-nine million seven hundred ninety-two thousand four hundred fifty-eight, period and T to one over frequency, direction to frequency_to_wavelength or wavelength_to_frequency, formula to the matching identity string, equation to a filled substitution line, unit labels for each quantity, message to a short English summary, and steps to an ordered array of calculation lines. Pricing is a flat $0.002 per successful request with unit item and zero marginal unit price.
Practical tips, limits, and related searches
When teaching, pair examples: frequency one times ten to the eight hertz yields wavelength about two point nine nine eight metres; wavelength three metres yields frequency about ninety-nine point nine three megahertz; and frequency zero demonstrates the hard invalid_input path that protects callers from division by zero. Failed tasks that return invalid_input do not consume prepaid balance, which keeps exploratory scripts cheap when learners deliberately send zero.
Integration use cases
Homework and exam wavelength checks
Students enter f or λ from textbook RF problems and compare hand-written c/f results and period against a deterministic API response before submitting.
Unit tests for RF utility libraries
Generate known-good frequency-to-wavelength and wavelength-to-frequency pairs plus deliberate zero-input rejections for firmware or Python helper expected values.
Technical questions
Can I send both frequency and wavelength?
No. Provide exactly one field. Sending both returns invalid_input so the conversion direction stays unambiguous.