Enter the frequency of a sine wave below to find the Nyquist rate.
FN = 2*F
FN is the Nyquist Rate
F is the Input Frequency
The Nyquist rate for a sine wave with frequency 10 kHz is 20 kHz or 20 kSPS (kilo-samples-per-second). Sampling at a rate that is greater than or equal to this value will ensure that the sine wave can be accurately represented.
What is the Nyquist Rate for a Square Wave?
A square wave consists of many harmonics (in theory an infinite number). It is represented as the sum of sine waves with decreasing amplitude. Use this calculator to find the harmonic frequencies and amplitudes.
The relative signal level of the 11th harmonic is 20 dB lower than the fundamental. As the harmonic number increases, the level continues to decrease.
So it would be safe to say that the Nyquist frequency of a square wave can be calculated by entering the 11th harmonic frequency into the calculator. For instance the Nyquist Rate for a 1 kHz square wave is 22 kHz.
Nyquist Rate vs Nyquist Frequency
These two quantities are often confused for one another. What’s the difference?
Nyquist rate is the minimum rate at which a signal should be sampled (using an Analog-to-digital converter for instance) such that it can be reconstructed without errors.
Nyquist frequency is the maximum frequency of an input sinusoidal signal for a given sampling rate.
 Nyquist Rate on Wikipedia