Online Tool Store
Doppler Shift Calculator
Enter a source frequency, wave speed, and relative velocity to calculate the Doppler-shifted observed frequency for sound or light.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
343 m/s = speed of sound in air at 20°C.
Observed frequency
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How Doppler Shift Calculator works
- Enter the source's emitted frequency and the speed the wave travels through its medium (e.g. 343 m/s for sound in air).
- Enter how fast the source is moving and whether it's approaching or receding.
- Enter how fast the observer is moving and whether they're approaching or receding.
- The observed frequency, and how far it shifted from the source frequency, update instantly.
The formula
The classical Doppler effect for a wave through a medium is:
f_observed = f_source × (v_wave ± v_observer) / (v_wave ∓ v_source)
The observer term uses + when the observer moves toward the source and − when moving away; the source term uses − when the source moves toward the observer and + when moving away. Example: a 440 Hz source approaching at 30 m/s through air (343 m/s) with a stationary observer gives 440 × 343 / (343 − 30) ≈ 483.13 Hz — a noticeably higher pitch.
FAQ
Which direction should I pick for the source and observer?
Pick "Approaching" if that object is moving toward the other one (frequency rises), or "Receding" if it is moving away (frequency drops). The two toggles are independent — a source can approach while the observer stands still, or both can move in either direction.
Why does the calculator reject a source speed equal to or above the wave speed?
The formula divides by (wave speed ∓ source speed). At or above the wave speed that denominator hits zero or goes negative, which is the supersonic/sonic-boom regime — a different, non-linear situation this simple Doppler formula does not model.
Does this work for light as well as sound?
The classical formula here is accurate for sound and other waves through a medium at everyday speeds. For light, the same shape approximates the result only at speeds much slower than light; true relativistic Doppler shift needs a Lorentz factor this calculator does not include.
How we compare
| Feature | Online Tool Store | Doing it by hand | A physics simulator app |
|---|---|---|---|
| Independent approach/recede toggle for both source and observer | ✓ | Easy to mix up the ± signs | ✓ |
| No install, runs in your browser | ✓ | N/A | ✗ |
| Free, no sign-up | ✓ | ✓ | ✗ |
Working through the ± sign convention by hand is where most manual Doppler calculations go wrong — Doppler Shift Calculator handles the direction logic for you and shows the shifted frequency and percentage change immediately, without installing a full physics simulator for a single calculation.