About the Doppler Effect Calculator
What is the Doppler Effect Calculator?
The Doppler effect is the change in pitch you hear as a siren approaches and then moves away. Waves bunch up in front of a moving source and spread out behind it.
Enter the source frequency, the wave speed and the speeds of the source and observer towards each other.
How to use the Doppler Effect Calculator
- Source Frequency (Hz) (sample: 1,000)
- Wave Speed (m/s) (sample: 343)
- Source Speed towards the Observer (m/s, negative if moving away) (sample: 20)
- Observer Speed towards the Source (m/s, negative if moving away) (sample: 0)
- Press Calculate Doppler Shift (results also refresh as you type). The result card shows the Observed Frequency, along with Frequency shift, Shift in percent and Pitch.
Formula used
f′ = f × (v + v_o) ÷ (v − v_s)
- v = speed of the wave (343 m/s for sound in air)
- v_o, v_s = observer and source speeds, positive when moving towards each other
For light and other electromagnetic waves, a relativistic formula is used instead.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Source Frequency (Hz) | 1,000 |
| Wave Speed (m/s) | 343 |
| Source Speed towards the Observer (m/s, negative if moving away) | 20 |
| Observer Speed towards the Source (m/s, negative if moving away) | 0 |
| Result | Value |
|---|---|
| Observed Frequency | 1,061.92 Hz |
| Frequency shift | 61.92 Hz |
| Shift in percent | 6.19% |
| Pitch | Higher – approaching |
Tips for using the Doppler Effect Calculator
- Police speed guns and weather radar use the Doppler shift of radio waves.
- Astronomers measure the redshift of galaxies with the same principle.