# Doppler Effect Calculator

URL: https://speedycalculator.com/calculators/physics/doppler-effect/
Last updated: 2026-10-25

> The Doppler effect calculator finds the frequency heard when a sound source and listener move toward or away from each other, such as a passing ambulance siren.

## Inputs

- Source frequency (Hz, kHz, MHz, GHz)
- Source speed toward listener (m/s, km/h, mph, ft/s, knots)
- Listener speed toward source (m/s, km/h, mph, ft/s, knots)
- Speed of sound (m/s, km/h, mph, ft/s, knots)

## Results

- Observed frequency
- After passing (moving apart)

## Formula

```
f′ = f × (v + v_observer) ÷ (v − v_source)   (positive speeds = moving toward each other)
```

## Explanation

Approaching sources sound higher and receding sources sound lower because the waves are bunched up or stretched out.

### How to use the Doppler Effect Calculator

- **Source frequency**
- **Source speed toward listener**
- **Listener speed toward source**
- **Speed of sound**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

The emitted frequency is scaled by the ratio of wave speeds relative to the observer and source.

### Inputs explained

FieldWhat to enterSource frequencyUnits: Hz, kHz, MHz, GHzSource speed toward listenerUnits: m/s, km/h, mph, ft/s, knotsListener speed toward sourceUnits: m/s, km/h, mph, ft/s, knotsSpeed of soundUnits: m/s, km/h, mph, ft/s, knots

### What each result means

- **Observed frequency** = [Source frequency] × ([Speed of sound] + [Listener speed toward source]) ÷ ([Speed of sound] - [Source speed toward listener])
- **After passing (moving apart)** = [Source frequency] × ([Speed of sound] - [Listener speed toward source]) ÷ ([Speed of sound] + [Source speed toward listener])

### Example values

How the main result changes when **Source frequency** changes and everything else stays at the example values above:

Source frequency (Hz)Observed frequency (Hz)350377.52525566.27700755.03875943.791,0501,132.551,4001,510.06

## Worked example

Inputs — Source frequency: 700 Hz; Source speed toward listener: 25 m/s; Listener speed toward source: 0 m/s; Speed of sound: 343 m/s.

Results — **Observed frequency = 755.03 Hz**; After passing (moving apart) = 652.45 Hz.

## FAQ

**Does the Doppler effect apply to light?**
Yes; astronomers use redshift to measure how fast galaxies recede.

**What happens if the source moves faster than sound?**
A shock wave, the sonic boom, forms.

**What formula does the Doppler Effect Calculator use?**
f′ = f × (v + v_observer) ÷ (v − v_source)   (positive speeds = moving toward each other).