Return Loss Calculator

Convert between Return Loss (dB), VSWR, reflection coefficient (|Γ|), mismatch %, and impedance-based reflection. Includes Show Work and share links.

How to Use

  1. Select an input mode (Return Loss, VSWR, |Γ|, or Impedance).
  2. Enter the value(s) and units (dB, Ω, etc.).
  3. Outputs update instantly (without changing the page URL).
  4. Open “Show Work” for formulas and steps, or use Share Link to copy a restorable URL.
RF Match Lab View
Visual feedback: match quality, reflections, and quick readouts.
RL
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VSWR
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|Γ|
—
Mismatch
—
Quality: —
Inputs & Settings
Pick one input mode. The tool converts to the rest.
Tip: Use impedance mode when you know load impedance and line/system impedance (often 50Ω or 75Ω).
Higher dB = better match (less reflected power).
Some instruments report S11(dB) as a negative number; Return Loss is typically reported as a positive number.
Show Work (step-by-step)
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Work is shown using standard RF relationships. For impedance mode, complex arithmetic is shown in a readable format.

Formulas & Reference

Return Loss (positive dB): RL = −20 log10(|Γ|)

  • Reflection coefficient magnitude: |Γ| = 10^(−RL/20)
  • VSWR from |Γ|: VSWR = (1 + |Γ|) / (1 − |Γ|)
  • |Γ| from VSWR: |Γ| = (VSWR − 1) / (VSWR + 1)
  • Reflected power fraction (lossless): Pref / Pfwd = |Γ|²
  • Mismatch loss (dB): ML = −10 log10(1 − |Γ|²)
  • Impedance reflection (complex): Γ = (ZL − Z0) / (ZL + Z0)
Where Γ is the reflection coefficient and Z0 is the line/system impedance (often 50Ω or 75Ω).

FAQ

Is higher return loss better?

Yes. Higher Return Loss (in dB, positive) means lower reflections and a better impedance match.

Why do some meters show S11 as a negative dB number?

Many instruments report S11(dB) = 20 log10(|Γ|), which is negative when |Γ| < 1. “Return Loss” is often reported as the positive magnitude: RL = −S11(dB).

Can line loss affect return loss and VSWR?

Yes. Lossy transmission lines can reduce the measured reflected wave at the source end, making the match appear better than at the load. This tool uses standard lossless relationships unless you’re analyzing a full system with known line loss.

What’s a “good” return loss?

Rule-of-thumb: ~10 dB is usable, ~14 dB is decent, ~20 dB is good, and 30 dB+ is excellent (application dependent).

Tool Info

Last updated:

Updates may include unit support, improved impedance-mode work display, and edge-case handling.