Use this electronics calculation for a first-pass component, converter, signal, motor, or sensor estimate when the stated operating conditions and units match the device data.

Fundamental RMS amplitude

Required number input.

Harmonic RMS amplitudes

Required list input.

Calculate THD from RMS harmonic amplitudes relative to the fundamental: sqrt(sum of harmonic squares)/fundamental. Output is percent and dBc; include only the harmonics specified by the measurement method, excluding noise and DC. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

THD (%)

The resulting thd (%) returned as a number.

THD (dBc)

The resulting thd (dbc) returned as a number.

• ADC relationships often assume an ideal full-scale sine wave, uniform quantization, coherent sampling, and independently specified noise or jitter. Real ENOB, SNR, THD, SFDR, aperture uncertainty, reference noise, clock phase noise, input bandwidth, and coding conventions depend on the test setup and datasheet definition.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Check the result against the current datasheet and worst-case operating corners, then verify the circuit or measurement with simulation and bench testing where failure matters.

• THD Percent

  Compute total harmonic distortion in percent as 100 x sqrt(V2^2 + V3^2) / Vfundamental; harmonics must be non-negative and the fundamental positive.

• ADC Spurious-Free Dynamic Range

  Compute SFDR in dBc as 20log₁₀(fundamental RMS amplitude/largest spur RMS amplitude), excluding DC. Use amplitudes measured in the same unit from one spectrum.

• THD+N Percent

  Compute THD+N percentage from the RMS residual and fundamental as thdnPercent = sqrt(harmonicsAndNoiseV^2) / fundamentalV * 100.