Standing Wave Ratio (SWR) Calculator
Convert between SWR, reflection coefficient and return loss — or work it all out from your line and load impedances — with a conversion table, an SWR curve and a live standing-wave pattern.
SWR rises steeply as |Γ| approaches 1. The dot marks your operating point.
Voltage magnitude along the line (forward wave = 1). Peaks reach 1 + |Γ|, dips fall to 1 − |Γ|; their ratio is the SWR. The pattern's position shifts with the phase of Γ.
How to Use This Calculator
- Basic: type any one of SWR, |Γ| or return loss — the other two fill in instantly.
- Advanced: enter the line impedance Z₀, the load's resistance and reactance, and the forward power.
- Read the result card for SWR and a quick match-quality verdict.
- Study the graphs — the SWR curve and the standing-wave voltage pattern both update live.
- Use the conversion table for return loss, mismatch loss and reflected/transmitted power.
What This Tool Offers
- ✓Two-way conversion between SWR, |Γ| and return loss.
- ✓Complex load support — resistance plus reactance, with Γ magnitude and phase.
- ✓Conversion table — return loss, mismatch loss, reflected and transmitted power.
- ✓Two live graphs — SWR versus |Γ|, and the standing-wave envelope.
- ✓Power in mW, W, kW and dBm for forward, reflected and delivered power.
What is standing wave ratio?
When a transmission line is not terminated in its characteristic impedance, part of the forward wave reflects at the load and interferes with it, creating a standing wave. The SWR is the ratio of the maximum to the minimum voltage along the line. A perfect match gives 1:1; the larger the mismatch, the higher the SWR.
Formula
Rearranged: |Γ| = (SWR − 1) / (SWR + 1). The reflection coefficient itself is Γ = (ZL − Z₀) / (ZL + Z₀). Return loss is RL = −20·log₁₀|Γ| and mismatch loss is ML = −10·log₁₀(1 − |Γ|²).
| Symbol | Meaning |
|---|---|
| SWR | Standing wave ratio, Vmax / Vmin (≥ 1) |
| |Γ| | Magnitude of the reflection coefficient (0 to 1) |
| Z₀ | Characteristic impedance of the line |
| ZL | Load impedance, RL + jXL |
| RL | Return loss — how far below the forward wave the reflection is, in dB |
| ML | Mismatch loss — power lost to reflection, in dB |
Reference: SWR conversion values
| SWR | |Γ| | Return loss (dB) | Reflected power |
|---|---|---|---|
| 1.0 : 1 | 0 | ∞ | 0% |
| 1.1 : 1 | 0.048 | 26.4 | 0.2% |
| 1.2 : 1 | 0.091 | 20.8 | 0.8% |
| 1.5 : 1 | 0.200 | 14.0 | 4.0% |
| 2.0 : 1 | 0.333 | 9.5 | 11.1% |
| 3.0 : 1 | 0.500 | 6.0 | 25.0% |
| 5.0 : 1 | 0.667 | 3.5 | 44.4% |
| 10 : 1 | 0.818 | 1.7 | 66.9% |
Reference: common line impedances
| Line | Typical Z₀ |
|---|---|
| Coax (RF, ham, test gear) | 50 Ω |
| Coax (video, cable TV) | 75 Ω |
| Twin-lead | 300 Ω |
| Open-wire / balanced line | 450–600 Ω |
Frequently asked questions
Below about 1.5:1 is generally excellent and below 2:1 is good for most purposes. Around 3:1 many transmitters begin to fold back power, and above that losses and stress on the transmitter grow quickly.
On a lossless line, no — SWR is the same everywhere. On a real line, loss attenuates the reflected wave, so the SWR measured at the transmitter is lower than at the load.
SWR is Vmax/Vmin, and |Γ| ranges from 0 to 1, so the formula's value runs from 1 (no reflection) up to infinity (total reflection).
Assumes a lossless line and a single load; real systems also have cable loss and frequency-dependent impedance.
What it means
The standing wave ratio (SWR) is the ratio of the maximum voltage (or current) to the minimum along a transmission line. It is related to the reflection coefficient by SWR = (1 + |Γ|) / (1 − |Γ|). SWR = 1 means a perfect match (no standing wave). Higher SWR indicates mismatches and can lead to reduced power transfer and voltage breakdown. In practice, an SWR of 1.5:1 is often considered acceptable. Example: If |Γ| = 0.2, then SWR = (1+0.2)/(1−0.2) = 1.2/0.8 = 1.5. This is a typical value for a well‑matched antenna system. SWR is measured using a directional wattmeter and is used to tune antennas.
Worked example
Standing Wave Ratio – Practical Example
Real‑World| Parameter | Value |
|---|---|
| |Γ| | 0.2 |
| Formula | VSWR = (1 + |Γ|) / (1 − |Γ|) |
Common mistakes
Watch unit consistency and the assumptions behind the formula; misapplying it outside its valid conditions is the most frequent error.Applications
Standing wave ratio (SWR) = (1+|Γ|)/(1−|Γ|) measures the degree of mismatch on a transmission line. A SWR of 1 is ideal; higher values indicate poor matching. Engineers use it to check antenna systems, to adjust matching networks, and to ensure efficient power delivery. SWR is a key metric in RF communication systems.
- Antenna system tuning and performance verification
- Transmission line and cable fault detection
- RF amplifier and transmitter protection
- Impedance matching network adjustment
- Educational understanding of standing waves
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