Calculate the observed frequency, shift and wavelength from source and observer speeds using the Doppler effect.
Positive = moving toward; negative = moving away.
About this tool
Doppler Effect Calculator is a free, in-browser acoustics tool that finds the frequency an observer hears when the source, the observer, or both are moving. Enter the source frequency and the two speeds and it returns the observed frequency, the shift and the observed wavelength. Everything is computed locally in your browser.
It uses f' = f·(v + vₒ)/(v − vₛ), where v is the speed of sound, vₒ is the observer's speed toward the source and vₛ is the source's speed toward the observer. The speed of sound defaults to 343 m/s but can be derived from air temperature with v = 331.3 + 0.606·T. The observed wavelength follows from λ' = v/f'.
Use positive speeds for motion that reduces the distance (observer toward source, source toward observer) and negative for the opposite. The tool guards against v − vₛ ≤ 0, the point where a source reaches the speed of sound. Speeds are in m/s, frequency in hertz and wavelength in metres.
Frequently asked questions
What is the sign convention for the speeds?
Enter the source speed as positive when it moves toward the observer, and the observer speed as positive when it moves toward the source. Use negative values for motion the other way. This matches f' = f·(v + vₒ)/(v − vₛ).
How is the speed of sound handled?
It defaults to 343 m/s (about 20 °C air). Switch to temperature mode and the tool computes v = 331.3 + 0.606·T from the air temperature in Celsius, then uses that value throughout.
Why do I get a supersonic error?
If the source speed toward the observer reaches or exceeds the speed of sound, v − vₛ becomes zero or negative and the formula breaks down (a shock wave forms). Reduce the source speed below the speed of sound.
Does this cover light or just sound?
This calculator uses the classical acoustic Doppler formula for sound in a medium. The relativistic Doppler effect for light uses a different equation. All calculations here run in your browser and nothing is uploaded.