Doppler Effect Calculator
Find the shifted frequency of a moving siren or listener.
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Doppler Effect Calculator by TheCalcTools
How the Doppler Effect Calculator works
Enter the source frequency, the speed of the source toward the observer and the speed of the observer toward the source.
Use negative speeds for motion away.
The observed frequency changes by the ratio of the relative wave speeds.
The formula
Worked example
Using the default values shown in the calculator:
| Source frequency (Hz) | 440 |
|---|---|
| Source speed toward observer (m/s) | 30 |
| Observer speed toward source (m/s) | 0 |
| Wave speed (m/s) | 343 |
- An ambulance at 30 m/s approaches while emitting 440 Hz.
- f′ = 440 × 343 ÷ (343 − 30) = 482.17 Hz.
- The pitch rises by 42.17 Hz.
Result:
| Observed frequency (Hz) | 482.17 |
|---|---|
| Shift (Hz) | 42.17 |
| Observed wavelength (m) | 0.7114 |
Frequently asked questions
Why does a passing siren drop in pitch?
As it approaches, wavefronts are compressed (higher pitch). After it passes, they are stretched (lower pitch).
Does it apply to light?
Yes, with relativistic corrections. It gives redshift and blueshift in astronomy and is used in radar speed guns.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.