Total Harmonic Distortion Calculator
Calculate total harmonic distortion (THD%) from fundamental and harmonic amplitude values for audio and power systems.
What Is Total Harmonic Distortion?
Total harmonic distortion (THD) measures how much unwanted harmonic energy appears alongside a fundamental signal. Audio engineers, power electronics designers, and test labs use THD% to judge amplifier quality, inverter performance, and sensor linearity.
How THD Is Calculated
Square each harmonic amplitude, sum those squares, take the square root, then divide by the fundamental amplitude.
Multiply by 100 for THD percent. Lower values mean a cleaner waveform with less distortion.
Related tools: Harmonic Series Calculator and Note Frequency Calculator.
Frequently Asked Questions
What is the THD formula?
THD% equals the square root of the sum of squared harmonic amplitudes divided by the fundamental amplitude, times 100.
Which harmonics should I include?
Include every harmonic you can measure, starting with the 2nd. More harmonics give a fuller picture, especially for power systems.
What is a good THD value?
It depends on the application. High-end audio gear may target well below 0.1%, while industrial inverters might allow several percent.
Can THD be expressed in decibels?
Yes. THD in dB is 20 times the base-10 logarithm of the THD ratio. This calculator shows both percent and dB.
What units should amplitudes use?
Use the same unit for the fundamental and every harmonic, such as volts, amperes, or pascals. Only relative ratios matter for THD%.
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