VSWR Calculator

Work out vswr instantly with clear inputs, formula shown and shareable results.

About VSWR Calculator

The reflection coefficient is the square root of the reflected-to-forward power ratio, and VSWR is (1+rho)/(1-rho). A 2:1 SWR means rho = 0.333, so 11% of the power is reflected and only 0.5 dB is actually lost — much less alarming than the SWR figure suggests.

Formula

VSWR

rho = sqrt(Prefl / Pfwd); VSWR = (1 + rho)/(1 - rho); mismatch loss = -10 log10(1 - rho^2)

Worked example

With the default values below, VSWR Calculator returns VSWR of 1.50. Change any input above and every figure here is recalculated in your browser.

Inputs used

Forward power: 100 W
Reflected power: 4 W
System impedance: 50 Ω

Results

VSWR: 1.50 :1
Reflection coefficient: 0.20000
Return loss: 13.98 dB
Mismatch loss: 0.1773 dB

Step by step

1Values used
2VSWR
3VSWR= 1.50 :1
4Reflection coefficient= 0.20000
5Return loss= 13.98 dB
6Mismatch loss= 0.1773 dB

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Is 2:1 SWR a problem?

Not for power transfer — only 0.5 dB is lost. It matters because many transmitters fold back power or stress their output stage above about 1.5-2:1.

Does a low SWR mean a good antenna?

No. A resistor gives a perfect SWR and radiates nothing. SWR only tells you about the match, not the radiation efficiency.