SWR Calculator
Find standing wave ratio two ways: from measured forward and reflected power, or from the load and line impedance. The tool also returns the reflection coefficient and return loss in dB.
How to use the SWR calculator
- Pick your inputs: forward and reflected power, or load and line impedance.
- Enter the values, for example 100 watts forward and 4 watts reflected.
- Read the reflection coefficient, SWR and return loss.
Examples
From power readings
forwardPowerW = 100, reflectedPowerW = 4
reflection = 0.2, SWR = 1.5, return loss = 13.98 dB
From impedance
loadOhms = 75, lineOhms = 50
reflection = 0.2, SWR = 1.5
Frequently asked questions
How do I calculate SWR from forward and reflected power?
First find the reflection coefficient as the square root of reflected over forward power, then SWR = (1 + coeff) / (1 - coeff). With 100 watts forward and 4 watts reflected the coefficient is 0.2 and SWR is 1.5.
How do I calculate SWR from impedance?
The reflection coefficient is the absolute difference of load and line impedance over their sum, coeff = |Zload - Zline| / (Zload + Zline). A 75 ohm load on a 50 ohm line gives 0.2, which is an SWR of 1.5.
What is a good SWR?
An SWR of 1.0 is a perfect match. Many operators aim for 1.5 or lower, and most radios are happy below 2.0. Above 2.0 a tuner or matching change is usually worth it.
What is return loss?
Return loss is how much weaker the reflected wave is than the forward wave, returnLossDb = -20 * log10(coeff). A higher number is better. An SWR of 1.5 is a return loss of about 13.98 dB.
What does a perfect match give for return loss?
A perfect match has a reflection coefficient of zero, so no power is reflected and the SWR is 1.0. Return loss is then infinite because there is no reflected wave to measure.
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