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SWR, Γ and return loss converter

One quantity, four ways of naming it

SWR, the magnitude of the reflection coefficient, return loss and the percentage of reflected power are the same number in different units. Instruments show one, handbooks print another, and arguments on the air proceed as though they were different things.

11.21.522.5345710goodworkablebad
On the left a matched load, on the right almost total reflection
What to enter
Value
System impedance Z₀ (Ω)
Result
SWR
Magnitude of the reflection coefficient |Γ|
Return loss
Reflected power
Delivered to the load
Mismatch loss
Load impedance giving this SWR

📐 The formulas​

Γ = (SWR − 1) / (SWR + 1)        SWR = (1 + |Γ|) / (1 − |Γ|)
RL[dB] = −20 · log10|Γ|          |Γ| = 10^(−RL/20)
Reflected, % = 100 · |Γ|²
Mismatch loss: ML[dB] = −10 · log10(1 − |Γ|²)
From impedance: Γ = (Z − Z₀) / (Z + Z₀)

A table for quick reference:​

SWR|Γ|RL, dBReflected, %ML, dB
1.10.04826.40.230.010
1.50.20014.04.00.177
2.00.3339.511.10.512
3.00.5006.025.01.249
5.00.6673.544.42.553
Where this calculator stops:
  • The calculation uses the magnitude of the reflection coefficient: phase does not enter into it, so the load impedance is ambiguous
  • A given SWR is produced by two different resistances — Z₀·SWR and Z₀/SWR — and by an infinity of complex ones
  • Mismatch loss is not cable loss: the reflected power comes back to the transmitter
  • Return loss is always positive; a NanoVNA shows S11 with a minus sign, and it is the same number

🎯 In practice​

  • Reading a NanoVNA, which gives S11 in decibels when the figure you think in is SWR.
  • Checking against a specification written in return loss.
  • Deciding whether a fight is worth it: an SWR of 2.0 costs half a decibel, often less than the measurement error.
Practical advice:
  1. On the air, an SWR of 1.5 and one of 1.1 sound identical: the difference is 0.17 dB.
  2. With 75 Ω equipment, remember to change Z₀, or every figure will be wrong.
  3. If the SWR is perfect on every band, suspect the cable loss rather than the antenna.

© 2026 UR3PKI · CyberDev.Space · Content licensed under CC BY-NC-SA 4.0.

How to cite this calculator
UR3PKI. «SWR, Γ and return loss converter». CyberDev.Space. https://cyberdev.space/en/radio/calculators/lines/swr_converter (licence CC BY-NC-SA 4.0).

The licence lets you use this material freely, including in teaching materials, but only with attribution to the author and a link to the source.

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