Total Harmonic Distortion Calculator

Enter Signal Values

Enter the fundamental and harmonic amplitudes. Select whether the readings are RMS, peak, or peak-to-peak.

Fundamental Amplitude V1

Fundamental Frequency

Amplitude Type

Noise Amplitude

Load Resistance

Ohms

H2 Amplitude

H3 Amplitude

H4 Amplitude

H5 Amplitude

H6 Amplitude

H7 Amplitude

H8 Amplitude

H9 Amplitude

H10 Amplitude

Formula Used

Total Harmonic Distortion:

THD% = [√(V2² + V3² + V4² + ... + Vn²) / V1] × 100

Total Harmonic Distortion Plus Noise:

THD+N% = [√(V2² + V3² + ... + Vn² + Noise²) / V1] × 100

Signal to Noise Ratio:

SNR dB = 20 × log10(V1 / Noise)

SINAD:

SINAD dB = 20 × log10[V1 / √(Harmonics² + Noise²)]

All voltage values are converted to RMS before calculation. That keeps the ratio consistent and physically meaningful.

How to Use This Calculator

Enter the fundamental amplitude of the waveform.
Enter the fundamental frequency in hertz.
Select RMS, peak, or peak-to-peak input mode.
Enter harmonic amplitudes from the second to tenth order.
Add noise amplitude if your test includes a noise reading.
Enter load resistance for power estimates.
Press the calculate button.
Review THD, THD+N, SNR, SINAD, ENOB, and the harmonic chart.
Download the CSV or PDF report for records.

Example Data Table

Case	V1 RMS	H2 RMS	H3 RMS	H4 RMS	Noise RMS	Approx THD
Audio amplifier test	10.00 V	0.20 V	0.10 V	0.05 V	0.02 V	2.291%
Power inverter test	230.00 V	3.50 V	2.10 V	0.80 V	0.50 V	1.812%
Sensor output test	2.00 V	0.03 V	0.02 V	0.01 V	0.01 V	1.871%

Total Harmonic Distortion Guide

Understanding Distortion

Total harmonic distortion shows how much unwanted harmonic content exists in a periodic signal. A perfect sine wave has only one frequency. Real amplifiers, power supplies, speakers, and measurement chains add extra frequencies. These frequencies are integer multiples of the fundamental. The second harmonic is twice the base frequency. The third harmonic is three times the base frequency. The calculator compares those harmonic RMS values with the fundamental RMS value.

Why THD Matters

Low distortion helps a system reproduce a waveform with better fidelity. In audio, it means cleaner sound. In power systems, it can mean less heating, lower neutral current, and improved equipment life. In sensors and oscillators, it helps show linearity. THD is not the only quality metric. Noise, bandwidth, clipping, phase shift, and measurement method also matter. Still, THD is a fast way to compare designs.

How The Calculation Works

The tool squares each harmonic RMS value from order two through order ten. It adds those squared values. Then it takes the square root. This gives the combined harmonic RMS value. Dividing that value by the fundamental RMS value gives THD as a ratio. Multiplying by one hundred gives the percent result. If a noise value is entered, the tool also calculates THD plus noise. It then estimates SINAD and ENOB for deeper review.

Using Results Carefully

Always enter values from the same measurement method. Do not mix peak, peak to peak, and RMS values without selecting the correct input type. Use the same bandwidth for each reading. Check that the fundamental is not overloaded or clipped. A very small fundamental can make THD appear large. For lab reports, save the CSV file and keep the instrument settings. For design work, compare several loads, gains, and frequencies. The trend is often more useful than one number. If harmonic levels rise quickly with output, the system may be near saturation. If even harmonics dominate, asymmetry may be present. If odd harmonics dominate, clipping or nonlinear transfer may be likely. Use the graph to spot dominant orders quickly. A single large bar often points to one problem source. Balanced reductions across bars suggest wider overall circuit improvement.

FAQs

What is total harmonic distortion?

Total harmonic distortion is the ratio of combined harmonic RMS voltage to the fundamental RMS voltage. It shows how much a waveform differs from a clean sine wave because of extra harmonic frequency content.

Should I enter RMS or peak values?

You can enter RMS, peak, or peak-to-peak values. Select the correct input type. The calculator converts values to RMS before applying the distortion formulas.

What is a good THD value?

It depends on the system. Audio equipment often needs very low THD. Power equipment may allow higher values. Lower THD usually means a cleaner and more linear signal.

What is THD plus noise?

THD plus noise includes harmonic distortion and measured noise. It is useful when you want a broader signal quality figure instead of only harmonic distortion.

Why does the calculator ask for load resistance?

Load resistance lets the tool estimate power for the fundamental, harmonic content, and total signal. It is helpful for amplifiers, speakers, and power circuits.

Can I leave some harmonics as zero?

Yes. Leave unknown or insignificant harmonics as zero. For a stronger result, enter every harmonic measured by your analyzer within the selected bandwidth.

Why is my THD result very high?

High THD can happen when harmonics are large, the fundamental is small, or the signal is clipped. Check scaling, probe setup, gain, loading, and instrument bandwidth.

Can this calculator replace lab instruments?

No. It processes values you enter. Use a trusted analyzer or oscilloscope for measurement. This tool helps review, compare, report, and document those readings.