What this calculator does
Total Harmonic Distortion (THD) measures how much a signal (audio, power, or electrical) is distorted by unwanted harmonic frequencies compared to its clean fundamental tone. Lower THD means a cleaner, more accurate signal.
The formula
The standard definition is THD = √(V2² + V3² + V4² + … + Vn²) / V1 × 100%, where V1 is the amplitude of the fundamental frequency and V2 through Vn are the amplitudes of the 2nd, 3rd, and higher harmonics. This calculator supports up to the 5th harmonic.
THD is widely used to rate audio equipment and power electronics; very low THD (well under 1%) generally indicates high signal fidelity, though audibility of distortion also depends on which specific harmonics are present.
Last reviewed August 2026