How to Use Total Harmonic Distortion Calculator
Use the Total Harmonic Distortion Calculator to calculate THD percent, THD ratio, and THD in dB from a fundamental RMS value and harmonic RMS amplitudes.
- Prepare the input - Enter the RMS amplitude of the fundamental component H1. This value must be greater than zero because it is the reference denominator for THD.
- Choose the rule - Add each harmonic RMS amplitude as H2, H3, H4, and so on. Use the same measurement type and unit for every row, such as volts RMS or amps RMS.
- Check the result - Remove unused harmonic rows or leave only the measured harmonics. THD is based on the root-sum-square of the harmonics you provide.
- Use the output - Choose decimal places for reporting. Use more decimals for lab notes and fewer decimals for quick equipment comparison.
Formula & Theory - Total Harmonic Distortion Calculator
The Total Harmonic Distortion Calculator uses these rules:
THD ratio = sqrt(H2^2 + H3^2 + ... + Hn^2) / H1
THD percent = THD ratio x 100%
THD dB = 20 x log10(THD ratio)Total harmonic distortion compares all measured harmonic energy against the fundamental. Harmonics are combined by root-sum-square because RMS quantities represent power-related amplitudes; adding them directly would overstate distortion.
A lower THD percent indicates a cleaner waveform relative to its fundamental. The dB value is simply the same ratio expressed on a logarithmic amplitude scale. If harmonic values are zero, the ratio is zero and the dB result tends toward negative infinity.
Use Cases for Total Harmonic Distortion Calculator
The Total Harmonic Distortion Calculator is most useful in these concrete workflows:
- Checking audio amplifier distortion from measured harmonic voltages.
- Comparing power quality measurements in voltage or current waveforms.
- Documenting motor-drive, inverter, or signal-generator harmonic performance.
- Teaching the difference between individual harmonic amplitude and combined distortion.