Doppler Effect Calculator
Calculate the observed frequency of a moving sound source or observer with the Doppler effect formula — frequency shift, observed wavelength and pitch change, with speed in m/s, km/h, mph or knots.
Input
Frequency emitted by the source, in Hz.
In the speed unit below. 343 m/s is air at 20 °C.
Applies to all three speeds.
Output
| Metric | Value |
|---|---|
| No data yet | |
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/doppler-effect-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"frequency": "440",
"waveSpeed": "343",
"speedUnit": "m/s",
"sourceSpeed": "30",
"sourceDirection": "toward",
"observerSpeed": "0",
"observerDirection": "toward"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `doppler-effect-calculator` tool (Doppler Effect Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.
Embed widget
<iframe
src="https://iotools.cloud/embed/doppler-effect-calculator/"
width="100%" height="520" frameborder="0" scrolling="no" loading="lazy"
title="Doppler Effect Calculator — iotools.cloud"
sandbox="allow-scripts allow-forms allow-same-origin allow-downloads allow-popups allow-popups-to-escape-sandbox"
allow="clipboard-write"
style="width:100%;border:1px solid #e5e7eb;border-radius:12px;overflow:hidden"></iframe>
<script src="https://iotools.cloud/embed.js" async></script>Drop this into your own page — free, no key required, just a link back.
| Cost per API/MCP call | From 5 credits |
|---|---|
| Need more credits? | View pricing |
Also available with
Guides
Calculate the frequency a listener hears when the sound source, the listener, or both are moving. Handy for sirens, passing trains, physics homework and sound design.
How to use it
- Enter the source frequency in Hz and the speed of sound (343 m/s is air at 20 °C).
- Pick a speed unit — m/s, km/h, mph or knots.
- Enter the source speed and whether it moves toward or away from the observer.
- Enter the observer speed and direction the same way. Leave it at 0 for a stationary listener.
The formula
f′ = f · (v + vₒ) / (v − vₛ)
Here v is the speed of sound, vₒ the observer's speed toward the source (negative if moving away) and vₛ the source's speed toward the observer (negative if moving away). Approaching sources sound higher-pitched; receding ones lower.
Limits
If the source moves toward the observer at or above the speed of sound, a shock wave (sonic boom) forms and the formula no longer applies — the calculator tells you so rather than returning a meaningless number. The same applies to an observer outrunning the wave.
Other waves
The same formula applies to any wave in a medium — set the wave speed to that of water waves or ultrasound in tissue, for example. It does not apply to light, which needs the relativistic Doppler formula.