This VSWR calculator finds the voltage standing wave ratio from the load and line impedance, or from the reflection coefficient. Enter your values above to check antenna and feedline matching.
Formulas
Reflection Γ = (ZL − Z0) ÷ (ZL + Z0) VSWR = (1 + |Γ|) ÷ (1 − |Γ|)
Example
ZL = 75 Ω, Z0 = 50 Ω: Γ = 25 ÷ 125 = 0.2, so VSWR = 1.2 ÷ 0.8 = 1.5:1.
A VSWR of 1:1 is a perfect match; below 2:1 is acceptable for most antennas.
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Frequently Asked Questions
What is a good VSWR?
1:1 is ideal. Most antennas work well below 2:1, where reflected power stays low.
How do I calculate VSWR from impedance?
Find the reflection coefficient from the impedances, then VSWR = (1 + magnitude) / (1 – magnitude).
Does high VSWR damage a transmitter?
It can. High VSWR reflects power back to the transmitter, raising heat and stress on the final stage.