VSWR Calculator
Enter your forward and reflected power readings to get VSWR, return loss, reflection coefficient, and a meter showing where your antenna system sits.
SWR and VSWR are the same measurement
You will see both terms used, often on the same page, and they refer to the same thing in practice. VSWR is voltage standing wave ratio, the precise term, because the ratio is measured between voltage peaks and valleys on the line. SWR is the shorthand nearly everyone actually says. A meter reading 1.5:1 means the same whichever label is printed on it, so there is nothing to convert between them.
Standing wave ratio measures how well your antenna system is matched to your transmitter and feed line. When the impedance of your antenna matches the impedance of your coax, typically 50 ohms, all the power from your transmitter reaches the antenna and is radiated. The ratio in that ideal case is 1.0:1.
When there is a mismatch, some power is reflected back down the coax toward your radio. The interaction between the forward and reflected waves creates standing waves on the feed line, and the ratio between the voltage peaks and valleys is what this calculator reports.
The SWR Formula
SWR is calculated from the reflection coefficient (Gamma): SWR = (1 + Gamma) / (1 - Gamma), where Gamma = sqrt(Pr / Pf). Pf is your forward power and Pr is reflected power, both in watts.
Worked example: With 100W forward and 4W reflected, Gamma = sqrt(4/100) = 0.2. SWR = 1.2 / 0.8 = 1.5:1. Return loss is -10 x log10(0.04) = 14 dB, meaning only 4% of your power is wasted.
SWR Zones Explained
What your SWR reading means for your equipment and signal:
| SWR Range | Zone | Power Reflected | Practical Meaning |
|---|---|---|---|
| 1.0 - 1.5 | Excellent | < 4% | Negligible mismatch. All rigs operate at full power. |
| 1.5 - 2.0 | Acceptable | 4 - 11% | Minor mismatch. Some rigs may fold back power slightly. |
| 2.0 - 3.0 | Investigate | 11 - 25% | Significant power loss. Check antenna and coax. |
| 3.0+ | Danger | 25%+ | Most rigs shut down. Risk of damage on older equipment. |
When to Worry About SWR
Most stock antennas on handheld radios are tuned for the 2m and 70cm bands and will show reasonable SWR out of the box. Problems usually appear when you're operating at the edges of a band, using an antenna not designed for your frequency, or when connectors and coax have degraded over time.
Common causes of high SWR: corroded or loose connectors, water intrusion in the coax, an antenna that's too long or too short for the operating frequency, and using the wrong type of coax connector or adapter. An antenna analyzer is the single best diagnostic tool for tracking down SWR issues.
Upgrading your antenna? See our best handheld radios for beginners to find a rig that handles antenna swaps well.
Frequently Asked Questions
What is the difference between SWR and VSWR?
There is no practical difference. VSWR stands for voltage standing wave ratio and is the precise term, because the ratio is measured between voltage peaks and valleys on the feed line. SWR is the shorthand most operators use in conversation. A meter reading 1.5:1 means the same thing whichever label is printed on it, and there is nothing to convert between the two.
How do you calculate VSWR from forward and reflected power?
First take the square root of reflected power divided by forward power. That gives you the reflection coefficient, usually written as the Greek letter gamma. Then VSWR equals (1 + gamma) divided by (1 - gamma). For example, 100 watts forward and 4 watts reflected gives a reflection coefficient of 0.2, and a VSWR of 1.5:1. The calculator above does this for you.
What is a good SWR for ham radio?
An SWR below 1.5:1 is excellent and means your antenna is well-matched to your feed line. Most radios operate safely up to 2.0:1. Above 3.0:1, most modern rigs will automatically reduce power or shut down to protect their final amplifier transistors.
Can high SWR damage my radio?
Modern radios have built-in SWR protection circuits that fold back power or shut down the transmitter when SWR is too high. Older rigs without this protection can suffer damage to their final amplifier transistors from sustained high-SWR transmission. Always resolve SWR issues before transmitting at full power.
How do I lower my SWR?
Start by checking all coax connections for tightness and corrosion. Ensure your antenna is cut to the correct length for your operating frequency. Use an antenna analyzer to identify whether the antenna is too long or too short, then trim or extend accordingly. Also check your coax for damage or water intrusion.