Doppler Effect Calculator

How it is calculated

For sound in air the tool fixes the speed of sound at c = 343 m/s and computes f' = f × (c + vo) ÷ (c − vs). Here f is the source frequency in Hz, v_s is the source speed and v_o the observer speed, both in m/s. A positive v_s means the source moves toward the observer, a positive v_o means the observer moves toward the source; negative values mean moving away. The movement is assumed along the line joining them. If v_s equals 343 the formula divides by zero and no result is given. The answer is shown in Hz with two decimals. Another medium or temperature changes c.

Common mistakes

• Getting the sign wrong. Positive source speed means approaching; entering it as positive for a receding source gives a pitch that moves the wrong way.
• Entering speeds in km/h. Both speeds must be in m/s; 108 km/h is 30 m/s.
• Using this for light or radar. The constant 343 m/s is the speed of sound in air at about 20 °C, so it does not apply to electromagnetic waves, or to sound in water or at very different temperatures.
• Entering a source speed at or above 343 m/s. That is supersonic motion, where this formula no longer describes what a listener hears.