Doppler Effect Calculator
Observed frequency shift from relative motion.
Enter your values
Enter the source frequency in Hz.
Enter the source speed in m/s, + toward listener.
Enter the observer speed in m/s, + toward source.
Enter the speed of sound in m/s.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Observed frequency
- 467.2 Hz
- Frequency shift
- 27.2 Hz
- Percent shift
- 6.2%
Quick answer
Observed frequency = source frequency x (v_sound +/- v_observer) / (v_sound -/+ v_source).
f' = f (v +/- vo)/(v -/+ vs)
At a glance
| What it does | Observed frequency shift from relative motion. |
|---|---|
| Category | Physics |
| Inputs needed | Source frequency, Source speed, Observer speed, Speed of sound |
| Main output | Observed frequency |
| Formula | f' = f (v +/- vo)/(v -/+ vs) |
| Cost | Free — no sign-up, no download |
How to use the Doppler Effect Calculator
- 1Enter the source frequency and the speed of sound (343 m/s in air at room temperature).
- 2Enter source and observer speeds, positive when moving toward each other.
- 3Read the observed frequency and the amount of shift.
Inputs explained
- Source frequency(Hz)
- Enter the source frequency in Hz.
- Source speed(m/s, + toward listener)
- Enter the source speed in m/s, + toward listener.
- Observer speed(m/s, + toward source)
- Enter the observer speed in m/s, + toward source.
- Speed of sound(m/s)
- Enter the speed of sound in m/s.
Worked example
Using the values the calculator loads with:
Inputs
- Source frequency440 Hz
- Source speed20 m/s, + toward listener
- Observer speed0 m/s, + toward source
- Speed of sound343 m/s
Results
- Observed frequency467.2 Hz
- Frequency shift27.2 Hz
- Percent shift6.2%
Frequently asked questions
Why does a siren pitch drop as it passes?
As the ambulance moves away, sound waves stretch out, lowering the observed frequency.
Does this work for light?
Light uses a relativistic Doppler formula instead; this tool is for sound waves.
What do I need to enter into the Doppler Effect Calculator?
Just 4 values: source frequency, source speed, observer speed, speed of sound. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Doppler Effect Calculator work out the answer?
Observed frequency = source frequency x (v_sound +/- v_observer) / (v_sound -/+ v_source). It applies the formula f' = f (v +/- vo)/(v -/+ vs) and shows the working so you can check each step by hand.
Is the Doppler Effect Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.