VSWR Calculator

About this calculator

Voltage standing wave ratio is calculated as VSWR = (1 + |Γ|) / (1 − |Γ|), where Γ is the complex reflection coefficient produced when a transmission line's impedance doesn't match the load — typically an antenna. A perfectly matched system has Γ = 0 and VSWR = 1:1, meaning no power reflects back toward the source, while higher VSWR values indicate standing waves caused by reflected energy bouncing between source and load.

RF and antenna engineers measure VSWR to verify that a transmission line, connector or antenna is properly matched before transmitting at power, since a poor match reflects energy back into the transmitter, wastes power and can overheat or damage amplifier components. Amateur radio operators, cellular site technicians and satellite communications engineers routinely check VSWR with a directional coupler or antenna analyzer, generally aiming to stay below 2:1 for efficient operation.