The ratio of the sum of the magnitudes of the incident and reflected power to the difference of the magnitudes of the incident and reflected power at a point on a transmission line, expressed as a ration of n : 1:
VSWR = {|Vinc| + |Vrefl|} / {|Vinc| - |Vrefl|} : 1

VSWR is an indicator of impedance match. A VSWR of 1:1 represents a perfect match; infinite:1 a perfect mismatch or reflection. For good cascadability, the VSWR of a component should typically be better than 2:1.

VSWR can be translated into return loss using the equation
RL = 20 log10(VSWR)

It can be calculated from the reflection coefficient using the equation
VSWR = (1 + ||) / (1 - ||)