Impedance Matching Calculator

Enter a source (or transmission-line) impedance and a load impedance to compute the reflection coefficient, VSWR, return loss, and the percentage of power actually delivered to the load.

Quick Facts

Reflection coefficient
Gamma = (Z_L − Z0) / (Z_L + Z0)
VSWR = (1 + |Gamma|) / (1 − |Gamma|); a perfect match gives Gamma = 0 and VSWR = 1:1.
Common reference impedances
50 Ω (RF/coax) and 75 Ω (video/cable)
Connecting the two standards directly, with no matching network, is a frequent source of reflections.

Your Results

Calculated
Reflection coefficient |Γ|
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0 = perfect match, 1 = total reflection
VSWR
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Voltage standing wave ratio
Return loss
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Higher dB means a better match
Power delivered to load
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Share of incident power transmitted

Ready

Enter the source and load impedance, then press Calculate.

Understanding impedance matching

Impedance matching is the practice of making a load's impedance equal (or as close as practical) to the impedance of the source or transmission line feeding it, so that a signal or power source delivers its energy to the load instead of bouncing part of it back where it came from. It matters anywhere a signal travels along a defined-impedance path — coaxial cable feeding an antenna, a transmission line feeding an amplifier, audio gear, or high-speed digital traces — because any mismatch reflects a portion of the incident wave back toward the source.

The formulas

For a source or line impedance Z0 (assumed real) driving a load impedance Z_L = R_L + jX_L, four values describe the match:

  • Reflection coefficient: Γ = (Z_L − Z0) / (Z_L + Z0). Its magnitude |Γ| runs from 0 (perfect match) to 1 (total reflection, as with an open or short circuit).
  • VSWR (voltage standing wave ratio): VSWR = (1 + |Γ|) / (1 − |Γ|). A perfect match gives VSWR = 1:1; VSWR grows without bound as |Γ| approaches 1.
  • Return loss: Return loss (dB) = −20 × log10(|Γ|). Unlike most "loss" figures, bigger is better here — it means less power came back.
  • Power delivered: the fraction of incident power that reaches the load is 1 − |Γ|², so delivered power = incident power × (1 − |Γ|²); the rest is reflected.

Maximum power transfer

The maximum power transfer theorem states that a source delivers the most power to a load when the load impedance equals the complex conjugate of the source impedance (Z_L = Z0*). For the common case of a purely resistive source or transmission line (Z0 real, no reactance), that condition simplifies to Z_L = Z0 with X_L = 0 — a purely resistive load equal to the line impedance. This calculator assumes a real Z0, which covers the vast majority of coax, cable, and line-driver situations; if the source itself has significant reactance, use its full complex conjugate as the matching target instead.

Common reference impedances

  • 50 Ω — the standard for most RF equipment, Wi-Fi hardware, and general-purpose coaxial cable.
  • 75 Ω — the standard for video, cable TV, and satellite feeds; it minimizes loss for that application but is not directly compatible with 50 Ω gear without a matching pad or transformer.
  • 300 Ω — classic twin-lead television antenna feedline, now largely obsolete.
  • 600 Ω — a traditional reference impedance for telephone and audio transmission lines.

Frequently Asked Questions

What is the reflection coefficient?
The reflection coefficient Γ is Γ = (Z_L − Z0) / (Z_L + Z0), where Z0 is the source or transmission-line impedance and Z_L is the load impedance. Its magnitude ranges from 0 (a perfect match, no reflected power) to 1 (total reflection, as with an open or short circuit).
What is VSWR and how does it relate to the reflection coefficient?
VSWR (voltage standing wave ratio) is calculated as VSWR = (1 + |Γ|) / (1 − |Γ|). A perfect match gives VSWR = 1:1. Most RF systems treat VSWR at or below 1.5:1 as a good match, 1.5:1 to 2:1 as an acceptable but noticeable mismatch, and above 2:1 as poor enough to warrant a matching network.
What is return loss?
Return loss in decibels is −20 × log10(|Γ|). Unlike most loss figures, a higher return loss in dB is better: it means less power is reflected. A perfect match has infinite return loss, while a dead short or open has 0 dB return loss (all power reflected).
How much power actually reaches the load?
The fraction of incident power delivered to the load is 1 − |Γ|², with the remainder reflected back toward the source. For example, a VSWR of 2:1 (|Γ| ≈ 0.333) delivers about 89% of the incident power and reflects about 11%.

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