Alternating Current
Total Harmonic Distortion Calculator
The purpose of Total Harmonic Distortion is to turn RMS of harmonic components and fundamental RMS value into total harmonic distortion. Keep the source condition with the saved result so later comparisons remain meaningful.
Enter values for Total harmonic distortion
Use measurements from one operating condition.
Formula used on this page
This page evaluates THD = harmonic RMS ÷ fundamental RMS × 100. Only RMS of harmonic components and Fundamental RMS value enter the numerical result.
For the example shown, total harmonic distortion equals 5.22%. Treat that value as a demonstration, not a recommendation.
Calculate THD from combined harmonic RMS. When capacitive reactance affects the next decision, use Capacitive Reactance Calculator.
Sensitivity check
Change RMS of harmonic components from 12 V to 14.399999999999999 V while preserving the other measurements. The output changes from 5.22% to 6.26%.
The comparison demonstrates sensitivity, not a guaranteed field response.
Input notes
Use RMS values unless an input explicitly requests peak amplitude. Do not combine a worst-case value with unrelated nominal data.
Values used below a division bar must stay positive. A prefix error can move the result by several orders of magnitude.
- RMS of harmonic components
- Default example: 12 V. Enter RMS of harmonic components in V.
- Fundamental RMS value
- Default example: 230 V. Enter fundamental RMS value in V.
Checks that catch bad inputs
Mixing nominal and measured data is a common source of error.
Trace an unexpected result back through the raw entries first.
Interpreting the answer
The calculated Total harmonic distortion is meaningful only with its input conditions attached. Compare it with the applicable line-to-line or line-to-neutral limit.
Keep the input set beside the output so another reader can reproduce it.
Where this estimate can fail
The harmonic input must exclude the fundamental component.
Additional checks may be needed for harmonics, phase imbalance, saturation, and nonsinusoidal current. Document which effects were checked elsewhere in the analysis.
Keep distorted-waveform measurements separate from sine-wave assumptions.
Using this result in a larger analysis
Begin by confirming RMS of harmonic components at the operating point represented by the other entries. Record whether it came from a meter, nameplate, data sheet, or design assumption.
After calculating total harmonic distortion, compare its magnitude with impedance, phase, waveform, and equipment ratings. An independent order-of-magnitude check can reveal a misplaced decimal or unit prefix.
If uncertainty remains, calculate labeled low and high cases. Include frequency-dependent loss, parasitics, and waveform distortion when those effects can change the decision.