SWR Calculator
Turn SWR into return loss, reflected power and mismatch loss — or work out SWR from forward and reflected watts.
Formulas used
- Reflection coefficient:
|Γ| = (SWR − 1) ÷ (SWR + 1) - Return loss:
−20 · log₁₀|Γ|dB - Mismatch loss:
−10 · log₁₀(1 − |Γ|²)dB - SWR from power:
(1 + √(Pr/Pf)) ÷ (1 − √(Pr/Pf))
SWR reference table
| SWR | |Γ| | Return loss | Reflected | Mismatch loss |
|---|---|---|---|---|
| 1.1:1 | 0.048 | 26.4 dB | 0.2% | 0.01 dB |
| 1.2:1 | 0.091 | 20.8 dB | 0.8% | 0.04 dB |
| 1.3:1 | 0.130 | 17.7 dB | 1.7% | 0.07 dB |
| 1.5:1 | 0.200 | 14.0 dB | 4.0% | 0.18 dB |
| 1.7:1 | 0.259 | 11.7 dB | 6.7% | 0.30 dB |
| 2.0:1 | 0.333 | 9.5 dB | 11.1% | 0.51 dB |
| 2.5:1 | 0.429 | 7.4 dB | 18.4% | 0.88 dB |
| 3.0:1 | 0.500 | 6.0 dB | 25.0% | 1.25 dB |
| 4.0:1 | 0.600 | 4.4 dB | 36.0% | 1.94 dB |
| 5.0:1 | 0.667 | 3.5 dB | 44.4% | 2.55 dB |
Mismatch loss only describes the mismatch itself; real feedline loss rises with SWR on a lossy cable. Read more in our antenna & feedline guides.
Frequently asked questions
Is an SWR of 2:1 bad?
At 2:1 about 11% of the power is reflected and the mismatch loss is about 0.5 dB — a barely noticeable difference on the air. The bigger concerns are whether your transmitter starts folding back power and how much extra loss a long or lossy feedline adds.
Where should I measure SWR?
Measure at the transmitter for what the radio sees, but remember that feedline loss makes SWR look better at the shack end than it is at the antenna.
Does a tuner fix a high SWR?
A tuner matches the transmitter to the line so the radio sees a low SWR, but the mismatch between the line and the antenna is still there, along with any extra feedline loss it causes.