Total Harmonic Distortion Calculator

How to Use This Calculator

1. Enter the fundamental frequency amplitude (the main signal level).
2. Enter the amplitudes of harmonics (2nd, 3rd, 4th, 5th) if known (optional, leave 0 if unknown).
3. The calculator displays THD as a percentage and in decibels, plus a quality assessment.
4. Use this to measure audio quality, evaluate amplifiers, or analyze signal distortion.

THD Formula

Total Harmonic Distortion is calculated from fundamental and harmonic powers:

Example: Fundamental = 1V, 2nd harmonic = 0.05V, 3rd harmonic = 0.02V: THD = √((0.05² + 0.02²) / 1²) × 100 = √(0.0029) × 100 = 5.39%. THD (dB) = 20 × log₁₀(0.0539) = -25.4 dB.

Full Description

Total Harmonic Distortion (THD) is a measure of signal quality that quantifies how much a signal is distorted by harmonics (frequencies that are multiples of the fundamental frequency). THD is expressed as a percentage or in decibels, with lower values indicating better signal quality and less distortion. THD is critical in audio systems, amplifiers, and any application where signal fidelity is important.

Harmonic distortion occurs when signals pass through non-linear components (amplifiers, speakers, etc.), generating frequencies that are multiples of the fundamental. The 2nd harmonic is twice the fundamental frequency, the 3rd is three times, and so on. THD measures the total power of all harmonics relative to the fundamental. Lower THD means the signal is closer to the original, with less unwanted harmonic content.

This calculator helps you determine THD from fundamental and harmonic measurements. Enter the fundamental amplitude and harmonic amplitudes (if known), and it calculates THD percentage and decibels, plus a quality assessment. Use it to evaluate audio equipment, measure signal quality, analyze amplifiers, or understand how distortion affects signals. THD is a key specification in audio and RF systems.

Frequently Asked Questions