Physics
Instant, private, and free
Doppler Effect Calculator.
Calculate observed frequency using the signed source and receiver velocities in the classical wave model.
Set your values
Results update as you type.
Results update automatically as you type.
Educational model. Inputs and assumptions are explicit; verify engineering or scientific decisions independently.
Use Cases
Sound wave frequency shift
Determine the pitch change heard when a sound source (like a siren) and a listener move relative to each other. Useful for physics students and educators.
Example: A car horn at 500 Hz approaches you at 30 m/s; the observed frequency is higher.
Radar and sonar applications
Estimate the frequency shift in reflected waves for speed measurement or motion detection in educational or hobby projects.
Example: Measure the speed of a moving object by analyzing the frequency shift of a reflected wave.
Frequently Asked Questions
- What does the Doppler Effect Calculator do?
- It calculates the observed frequency of a wave when the source and receiver are moving relative to each other, using the classical (non-relativistic) Doppler formula. You input the source and receiver velocities (signed) and the emitted frequency, and it outputs the observed frequency.
- How do I enter velocities in this calculator?
- Velocities are signed: positive values typically indicate motion toward the receiver (for source) or toward the source (for receiver), while negative values indicate motion away. The calculator uses these signs to determine whether the observed frequency increases or decreases.
- Is this calculator suitable for light waves?
- No, this calculator uses the classical wave model, which is accurate for sound and other mechanical waves. For light or electromagnetic waves, relativistic effects must be considered, so this tool is not appropriate for those cases.
Tips & Common Mistakes
Tips
- Ensure you use consistent units for velocity (e.g., m/s) and frequency (Hz) to get accurate results.
- Remember that the sign of velocity matters: positive for motion toward the observer/source, negative for away.
- This calculator assumes the medium (e.g., air) is stationary relative to the observer; if the medium moves, results may differ.
- Double-check your input values: a common error is mixing up source and receiver velocities.
Common Mistakes to Avoid
- Forgetting to include the sign of velocity, which changes the direction of the frequency shift.
- Using the calculator for light waves, where relativistic Doppler formula is required.
- Entering velocities in different units (e.g., km/h vs m/s) without conversion, leading to incorrect results.
Last updated: August 13, 2026