The Doppler Effect Calculator is an online physics tool that helps determine the observed frequency of a sound when either the sound source or the observer is in motion. It uses the Doppler Effect formula f′=f×(v+vo)(v−vs)f’ = f \times \frac{(v + v_o)}{(v – v_s)}f′=f×(v−vs​)(v+vo​)​, where f′f’f′ represents the observed frequency, fff is the actual source frequency, vvv is the speed of sound in air, vov_ovo​ is the velocity of the observer, and vsv_svs​ is the velocity of the source. By entering these values, users can quickly find how the perceived sound changes as the source or observer moves toward or away from each other. This calculator is especially useful for students, teachers, and sound engineers who want to study or demonstrate how motion affects sound waves. Its clean design and instant calculation make it suitable for educational websites, physics projects, and learning environments.