About the Doppler Effect Calculator
When an ambulance comes towards you, its siren sounds higher, and when it passes and moves away the pitch drops. This is the Doppler effect. The calculator takes the true frequency of the source, the speed of sound, and the speed and direction of the source and the listener, and gives the frequency the listener hears, along with the change in hertz and in percent. Type the source frequency, the wave speed, and the speeds and directions of the source and listener and the Doppler shift appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Doppler Effect Calculator
- 1Enter the source frequency, the wave speed, and the speeds and directions of the source and listener.
- 2Pick the units or options from the menus if the Doppler shift tool offers them.
- 3Read the Doppler shift in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the Doppler shift
Physics students use it for wave problems, police use the same principle in radar speed guns, and doctors use it in ultrasound scans of blood flow. Astronomers use the equivalent formula for light to measure how stars move.
The pitch is higher on approach and lower on departure, with a sudden drop as the source passes. The shift is bigger the faster the source moves relative to the speed of sound. Motion of the listener also counts, but the effect is not symmetric.
How the Doppler shift is worked out
Observed frequency = source frequency × (wave speed + listener speed toward the source) ÷ (wave speed − source speed toward the listener). A siren at 440 Hz moving towards a still listener at 30 m/s (108 km/h) in air at 343 m/s is heard at 482.2 Hz, 42.2 Hz higher. When it moves away, the listener hears 404.6 Hz, 35.4 Hz lower.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Moving source and listener
- Direction choices
- Change in Hz and percent
Mistakes to avoid with Doppler shift
The source speed must be below the wave speed; at or above it, a sonic boom forms and this formula fails. The tool is for sound and other waves slower than light. For light from fast-moving objects, relativistic Doppler formulas are needed.
On phone and computer
On a phone, type into the boxes one after another and read the Doppler shift underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the Doppler shift move. The doppler effect calculator works the same on both. Sound and light work with waves. Use Wavelength Calculator and Frequency Converter for the numbers, Speed Calculator for the movement, and Decibel Calculator for loudness.
Features
- Source must be slower than the wave
- Approach raises the pitch
- Not for light at high speed
- Clear messages when the Doppler shift inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate Doppler shift?
Observed frequency = source frequency × (wave speed + listener speed toward the source) ÷ (wave speed − source speed toward the listener). A siren at 440 Hz moving towards a still listener at 30 m/s (108 km/h) in air at 343 m/s is heard at 482.2 Hz, 42.2 Hz higher. When it moves away, the listener hears 404.6 Hz, 35.4 Hz lower.
What is the formula for Doppler shift?
Observed frequency = source frequency × (wave speed + listener speed toward the source) ÷ (wave speed − source speed toward the listener). The doppler effect calculator applies it exactly and rounds only the displayed answer to six significant figures.
Why is the shift not symmetric for source and listener?
The medium carries the sound, so moving the source and moving the listener affect the wavelength in different ways.
What speed of sound should I use?
343 m/s for air at 20 °C. It rises by about 0.6 m/s for each degree of warming. In water it is about 1,480 m/s.
How do radar speed guns work?
They send out radio waves and measure the Doppler shift of the waves reflected by a moving car.
Is this doppler effect calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.