VSWR Calculator (Voltage Standing Wave Ratio)
Calculate the Voltage Standing Wave Ratio (VSWR) of an RF transmission line from impedance mismatch or from forward and reflected power readings.
What is VSWR?
Voltage Standing Wave Ratio (VSWR) describes how well an RF source, transmission line, and load (such as an antenna) are impedance-matched. A perfect match gives VSWR = 1:1, meaning no signal is reflected back toward the source. Higher VSWR values indicate more of the signal is reflected rather than radiated or absorbed, which wastes power and can stress the transmitter.
How this calculator works
You can calculate VSWR two ways. If you know the impedances, the reflection coefficient is |Γ| = |(ZL − Z0) / (ZL + Z0)|. If you instead measured forward and reflected power with a directional wattmeter, |Γ| = √(Preflected / Pforward). Either way, VSWR is then found from VSWR = (1 + |Γ|) / (1 − |Γ|), and the calculator also reports return loss in dB and the percentage of power reflected.
This tool is for general RF and antenna-system education and estimation. Real-world measurements can be affected by cable loss, connectors, and measurement accuracy.