Calculation sequence
Step-by-step method
- Divide RSS harmonic content by the fundamental RMS component.
- Multiply by 100 for THD.
- Combine fundamental and harmonic RSS for total RMS.
ElectricalAdvancedPower Quality
Total Harmonic Distortion Calculator
Calculate voltage or current THD from the fundamental RMS component and RSS harmonic content.
Why it matters: THD is a useful descriptor but does not replace the spectrum, TDD, measurement context, or point-of-common-coupling criteria.
Calculated result
Engineering evaluation
Total harmonic distortion (THD)10 %
- Total RMS quantity (Xᴿᴹˢ)
- 100.499 A
Engineering interpretation
The documented current components give 10% THD and 100.4988 A total RMS.
Important limitations
- No universal limit is applied. Spectrum, TDD, point of common coupling, voltage level, demand current, instrument bandwidth, and applicable IEEE criteria require review.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
THD = 100Xʰ/X₁
Xᴿᴹˢ = √(X₁²+Xʰ²)
Current substitution
THD = 100×10/100 = 10%; Xᴿᴹˢ = √(100²+10²) = 100.4988 A.
Equation legend
Inputs and calculated quantities
- X₁
- Fundamental RMS component — A or V
- Xʰ
- RSS harmonic content — A or V
- THD
- Total harmonic distortion — %
- Xᴿᴹˢ
- Total RMS quantity — A
Applications
How this calculation is used
Building design
Screen a documented harmonic measurement.
Construction
Check analyzer quantity type and bandwidth.
Commissioning
Calculate THD without applying a hidden universal limit.
Quality controls
Assumptions and limitations
Assumptions
- Harmonic components are orthogonal RMS quantities.
- Fundamental and harmonic RSS use the same unit and measurement interval.
Limitations
- No universal THD pass/fail threshold is applied.
- Harmonic spectrum, phase, interharmonics, TDD, point of common coupling, voltage level, and instrument method require IEEE and project review.
Field use
Verification procedure
- Follow the approved electrical-safety program and use correctly rated instruments.
- Confirm wiring, ratios, units, operating mode, and measurement boundaries.
- Document simultaneous readings and compare with approved project and manufacturer data.
Common engineering mistakes
- Combining values from different time intervals, phases, or measurement boundaries.
- Treating a screening result as equipment selection, protective-device coordination, or code compliance.
Technical basis
References and source standards
- IEEE Standards AssociationPower quantity, harmonic, transformer, motor, battery, and metering standards; verify the current applicable edition during professional review.
- NIST Guide for the Use of the International System of UnitsElectrical quantity, unit, symbol, and conversion context.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement