Speed of sound calculator
At 20 °C sound crosses dry air at about 343 m/s, compared with 331.3 m/s at 0 °C. Enter the air temperature in Celsius, Kelvin or Fahrenheit to get the speed of sound in metres per second and kilometres per hour. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Creativity
- 20
- Temperature c
- 20 C
- Temperature k
- 293.15
- Speed mps
- 343.2146226826
- Speed kmh
- 1,235.5726416572
Students checking homework on acoustics, teachers building answer keys, drone and aviation hobbyists estimating delay between a flash and a bang, game developers tuning distance cues, and engineers sanity-checking ultrasonic rangefinder assumptions all need a fast, deterministic number without opening a textbook table every time.
What the dry-air speed of sound formula means and which temperature to send
In an ideal dry-air model used throughout introductory physics and many engineering estimates, the speed of sound scales with the square root of absolute temperature. A standard classroom form anchors the constant so that at zero degrees Celsius the speed is three hundred thirty-one point three metres per second, written c equals three hundred thirty-one point three times the square root of T_K over two hundred seventy-three point fifteen.
Equivalently in Celsius theta you can write c equals three hundred thirty-one point three times the square root of one plus theta over two hundred seventy-three point fifteen. Search intent clusters around phrases such as speed of sound calculator, speed of sound in air, how fast does sound travel at twenty degrees, sonic speed temperature, and dry air sound velocity.
People want a numeric answer they can check against a worksheet, embed in a simulation, or feed into a larger pipeline—not only a reminder that sound is roughly three hundred forty-three metres per second at room temperature. Optional unit defaults to C for Celsius and also accepts celsius, K or kelvin, and F or fahrenheit. Units of the speed itself are always SI metres per second plus a convenience kilometres-per-hour field; there is no humidity table, no altitude correction, and no CO₂ adjustment—this product is the dry-air temperature model only.
How this calculator validates input and applies the square-root temperature model
Numeric strings that parse to finite numbers are accepted so forms and CSV-style pipelines can pass values without an extra cast. The unit field, when present, must normalize to Celsius, Kelvin, or Fahrenheit; unknown unit strings are rejected with a clear message. After parsing, the engine converts the input to absolute temperature in kelvin.
Any temperature at or below absolute zero—zero kelvin, minus two hundred seventy-three point fifteen Celsius, or minus four hundred fifty-nine point sixty-seven Fahrenheit—is rejected because the square-root model is undefined for non-positive absolute temperature and because absolute zero is a hard physical floor for thermal air models. Magnitudes above a published safety bound are also rejected to keep isolate arithmetic honest.
Practical use, limits, pricing, and delivery channels
Use the browser tool when you want an immediate speed-of-sound check while grading acoustics homework, estimating the lag between a lightning flash and thunder for a given air temperature, converting a lab temperature reading into a design speed for an ultrasonic sensor sketch, or verifying that a game or AR distance cue assumes a sensible room-temperature value.
Choose the temperature scale with the unit field: leave unit omitted or set C for everyday weather-style Celsius inputs, use K when your pipeline already works in absolute kelvin, and use F for Fahrenheit worksheets. Results are fully deterministic: the same temperature and unit always yield the same speeds and the same formula label. There is no language model, no external physics service, and no randomness, so the capacity is safe to pin in continuous-integration checks and reproducible lesson materials.
Pair it with a Doppler sound calculator when the next question is perceived frequency for a moving source, or with a generic wave-speed calculator when you already know frequency and wavelength instead of air temperature.
What you can do with it
Homework and lab acoustics drills
Students and graders compute dry-air sound speed for given classroom temperatures, with clear rejection when temperature is at or below absolute zero.
Sensor and rangefinder sanity checks
Ultrasonic and acoustic delay sketches convert a measured air temperature into a design speed without embedding a weather stack.
FAQ
What happens if temperature is below absolute zero?
Absolute zero and below are rejected because the dry-air square-root model needs strictly positive kelvin temperature.
Can I send Kelvin or Fahrenheit instead of Celsius?
Yes. Set unit to K or kelvin, or F or fahrenheit. If unit is omitted, temperature is interpreted as Celsius.
Is the speed of sound calculator free?
The browser tool runs free on your device.
Does this include humidity or altitude corrections?
No. This capacity models dry air from temperature only.
Why does sound travel faster in warm air?
Because in dry air the speed of sound grows with the square root of the absolute temperature. Warming the air from 0 °C to 20 °C takes the speed from 331.3 m/s to about 343 m/s.
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/speed-of-sound-air \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"temperature":20}'const res = await fetch("https://api.kit.forhosting.com/phys/speed-of-sound-air", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"temperature": 20
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/phys/speed-of-sound-air",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"temperature": 20
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/phys/speed-of-sound-air", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"temperature":20}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"temperature":20}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/phys/speed-of-sound-air", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"temperature": 20
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "phys.speed_of_sound_air",
"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
The speed of sound in dry air depends on absolute temperature: warmer air transmits pressure waves faster because the molecular speeds that set the bulk modulus and density ratio climb with the square root of kelvin temperature. This capability accepts air temperature in Celsius by default, or Kelvin or Fahrenheit via an explicit unit field, converts to absolute temperature, rejects values at or below absolute zero with a clear invalid_input error, and returns the dry-air speed in metres per second and kilometres per hour as structured JSON.
What the dry-air speed of sound formula means and which temperature to send
Send the required field temperature as a finite JSON number or numeric string; aliases t, temp, and capital T are accepted. The response echoes your input temperature and unit, reports temperature in both Celsius and Kelvin for cross-checks, and returns speed_mps and speed_kmh together with formula and method labels so downstream code can branch without sniffing shapes.
How this calculator validates input and applies the square-root temperature model
Send a JSON body with required temperature and optional unit. Missing temperature, empty strings, non-numeric text, NaN, and Infinity all fail immediately with invalid_input before any result is returned, and failed validation is not charged. On success the speed is computed as three hundred thirty-one point three times the square root of kelvin temperature over two hundred seventy-three point fifteen, then rounded to a stable decimal precision so the same input always yields the same JSON across JavaScript engines.
Practical use, limits, pricing, and delivery channels
Each successful request is one billable item at $0.002; failed validation—including absolute-zero and below—does not consume balance. Remember the model is dry air at the given temperature only: humidity, wind, and altitude can shift real outdoor measurements, but this endpoint deliberately returns the clean temperature-only dry-air figure used in textbooks and many engineering first estimates.
Integration use cases
Deterministic fixtures for physics tests
Pipelines that seed unit tests or interactive acoustics demos can call a pure dry-air oracle instead of reimplementing the sqrt-temperature formula in every language.
Technical questions
How do I calculate the speed of sound in dry air?
Send JSON with temperature set to the air temperature (for example temperature: 20 for 20 °C). The response includes speed_mps and speed_kmh using c=331.3*sqrt(T_K/273.15).