VSWR Voltage Standing Wave Ratio
Calculate VSWR, reflection coefficient, return loss, and mismatch loss from impedance or direct input. Free RF transmission line calculator with charts.
About This Calculator
The VSWR (Voltage Standing Wave Ratio) Calculator helps RF engineers, ham radio operators, and electronics designers compute key transmission line parameters. It supports three input modes: from load and characteristic impedance, from VSWR directly, or from return loss — making it versatile for both design and troubleshooting scenarios. The tool instantly calculates reflection coefficient (Γ), VSWR ratio, return loss (dB), mismatch loss (dB), and power transmission efficiency.
The core formulas used are: Reflection Coefficient Γ = |(ZL − Z0) / (ZL + Z0)| from impedance values, or Γ = (VSWR − 1) / (VSWR + 1) from VSWR, or Γ = 10(−RL/20) from return loss. VSWR is then computed as VSWR = (1 + |Γ|) / (1 − |Γ|). Return Loss RL = −20 × log₁₀(|Γ|) dB measures reflected power, while Mismatch Loss ML = −10 × log₁₀(1 − |Γ|²) dB quantifies power not delivered to the load. Power transmitted to the load is (1 − |Γ|²) × 100%.
Regional Notes
Global (IN/US/UK): VSWR and transmission line theory are universal — the formulas and standards (50Ω RF, 75Ω video, 600Ω audio) apply worldwide. The calculator uses unitless ratios and dB scales that are independent of regional conventions. Impedance values are always in ohms (Ω).
Frequently Asked Questions
What is VSWR and how is it calculated?
VSWR (Voltage Standing Wave Ratio) measures how efficiently RF power is transmitted to a load. It is calculated as VSWR = (1 + |Γ|) / (1 - |Γ|), where Γ is the reflection coefficient. A VSWR of 1:1 means perfect impedance matching with no reflected power.
What is a good VSWR value?
A VSWR of 1.5:1 or lower is considered excellent for most RF systems. Values between 1.5:1 and 2.5:1 are acceptable. Above 2.5:1 indicates significant mismatch where more than 18% of power is reflected, which can damage transmitters.
How do I calculate VSWR from impedance?
First calculate the reflection coefficient Γ = |(ZL - Z0) / (ZL + Z0)|, where ZL is the load impedance and Z0 is the characteristic impedance (typically 50Ω). Then VSWR = (1 + |Γ|) / (1 - |Γ|). For example, with ZL = 75Ω and Z0 = 50Ω, Γ = 0.2 and VSWR = 1.5:1.
What is the reflection coefficient?
The reflection coefficient (Γ) quantifies how much of an electromagnetic wave is reflected by an impedance discontinuity. It ranges from 0 (perfect match, no reflection) to 1 (open or short circuit, full reflection). It is the ratio of reflected wave amplitude to incident wave amplitude.
How is return loss related to VSWR?
Return Loss (RL) is the power loss of the reflected signal expressed in dB. It is calculated as RL = -20 × log₁₀(|Γ|). A high return loss (e.g. 30 dB) means very little power is reflected, corresponding to a low VSWR near 1:1. Return loss of 20 dB corresponds to VSWR of 1.22:1.
Can I use this calculator for any transmission line impedance?
Yes. Enter any load impedance (ZL) and characteristic impedance (Z0) values. Standard RF systems use 50Ω, video/cable TV uses 75Ω, and some audio systems use 600Ω. The calculator works for any impedance values including complex (resistive and reactive) loads.
What is mismatch loss in RF systems?
Mismatch Loss (ML) is the power lost due to impedance mismatch, calculated as ML = -10 × log₁₀(1 - |Γ|²). It represents power that is not delivered to the load because it reflects back to the source. Even a VSWR of 1.5:1 causes only 0.18 dB mismatch loss (96% power transmitted).