Total Harmonic Distortion Calculator
Find THD from the fundamental and harmonic amplitudes.
THD measures how much harmonic content distorts a signal away from a pure tone.
How the Math Works
Total Harmonic Distortion (THD) is calculated by comparing the combined power of all harmonic components to the fundamental frequency. The formula squares each harmonic amplitude (V2, V3, etc.), sums these squared values, takes the square root of that sum, and divides by the fundamental amplitude (V1). Multiplying by 100 converts the ratio to a percentage. For example, if your fundamental is 10V and harmonics total 2V, THD = sqrt(2^2)/10 * 100 = 20%.
Practical Applications
To use this calculator, measure or obtain the amplitude of your fundamental signal (V1) and all significant harmonic components (V2, V3, etc.) using an oscilloscope or spectrum analyzer. Enter these values into the calculator, ensuring you include all harmonics that contribute meaningfully to distortion. The result tells you what percentage of your signal's total amplitude comes from harmonic distortion rather than the intended fundamental frequency.
Day-to-Day Use
THD measurements help you understand the quality of audio signals in headphones, speakers, and amplifiers - lower distortion means clearer, more accurate sound reproduction. It's also crucial for electrical systems, where high THD in power supplies can cause equipment to overheat or malfunction, extending the lifespan of your electronics and improving energy efficiency in your home or workplace.
Worked example
Harmonics 0.5/0.3/0.1 on a 10 V fundamental give about 5.9%.
FAQ
What is good THD?
Hi-fi audio aims for well under 1%; lower means a cleaner signal.