SWR Power Loss Table
Reflected power loss as a function of SWR. Example column shows watts available from a 4 W transmitter. This only accounts for reflected power — it does not include cable loss, common-mode current, or RF choke dissipation.
Loss = P × ((SWR − 1)² / (SWR + 1)²)
| SWR | % Loss | % ERP | Watts (4 W TX) |
|---|---|---|---|
| 1.0:1 | 0.0% | 100.0% | 4.00 |
| 1.1:1 | 0.2% | 99.8% | 3.99 |
| 1.2:1 | 0.8% | 99.2% | 3.97 |
| 1.3:1 | 1.7% | 98.3% | 3.93 |
| 1.4:1 | 2.8% | 97.2% | 3.89 |
| 1.5:1 | 4.0% | 96.0% | 3.84 |
| 1.6:1 | 5.3% | 94.7% | 3.79 |
| 1.7:1 | 6.7% | 93.3% | 3.73 |
| 1.8:1 | 8.2% | 91.8% | 3.67 |
| 1.9:1 | 9.6% | 90.4% | 3.61 |
| 2.0:1 | 11.1% | 88.9% | 3.56 |
| 2.1:1 | 12.6% | 87.4% | 3.50 |
| 2.2:1 | 14.1% | 85.9% | 3.44 |
| 2.3:1 | 15.5% | 84.5% | 3.38 |
| 2.4:1 | 17.0% | 83.0% | 3.32 |
| 2.5:1 | 18.4% | 81.6% | 3.27 |
| 2.6:1 | 19.8% | 80.2% | 3.21 |
| 2.7:1 | 21.1% | 78.9% | 3.16 |
| 2.8:1 | 22.4% | 77.6% | 3.10 |
| 2.9:1 | 23.7% | 76.3% | 3.05 |
| 3.0:1 | 25.0% | 75.0% | 3.00 |
| 4.0:1 | 36.0% | 64.0% | 2.56 |
| 5.0:1 | 44.4% | 55.6% | 2.22 |
| 6.0:1 | 51.0% | 49.0% | 1.96 |
| 7.0:1 | 56.3% | 43.8% | 1.75 |
| 8.0:1 | 60.5% | 39.5% | 1.58 |
| 9.0:1 | 64.0% | 36.0% | 1.44 |
| 10.0:1 | 66.9% | 33.1% | 1.32 |
SWR ≤ 1.5:1 is generally safe for most transceivers. Above 2.0:1, many rigs reduce power automatically. Above 3.0:1, most rigs will fold back significantly or shut down. Data from Firestik — SWR Power Loss Table.