A phase constant represents the change in phase per unit length for a standing plane wave. The phase constant of a standing plane wave is denoted with the greek letter β (beta) and demonstrated the relationship between waveform cycles and wavelength. This quantity is often treated equally with a plane wave's wave number. However, this must be used with caution because the medium of travel changes this equality. Calculating the phase constant from frequency is a relatively simple mathematical operation.

Create an empty fraction.

Place 2π in the numerator.

Place the wavelength, often denoted as the Greek letter λ (Lambda), in the denominator.

Perform the indicated division and simplify as necessary. This final value is the phase constant of the plane wave being investigated.
References
 "Physics Principles with Applications, 6th Edition"; Douglas C. Giancoli; 2005
 Microwaves 101; Propagation Constant; PN Designs, Inc.; 2007