SWR, return loss and mismatch loss calculator

Type in any field: SWR, reflection coefficient, return loss, mismatch loss or reflected power. The others follow as you type.

Indicative calculation; verify before use.

SWR (VSWR)

: 1

Reflection coefficient |Γ|

0–1

Return loss

Mismatch loss

Reflected power

SWR

–

Power reaching the load

–

deliveredreflected

Return loss: –
S11 (same thing, negative sign): –
Mismatch loss: –
Reflection coefficient |Γ|: –
Reflected power: –

SWR from a power meter

Read forward and reflected power on an SWR/power meter (same units for both, e.g. watts).

Forward power

Reflected power

SWR: –
Reflected: –
Return loss: –
Net power (forward − reflected): –

Common SWR values

Tap an SWR value to load it.

SWR	\|Γ\|	Return loss	Reflected	Mismatch loss

How it works

|Γ| = (SWR − 1) / (SWR + 1) SWR = (1 + |Γ|) / (1 − |Γ|) RL = −20 × log10 |Γ| dB (S11 = −RL) reflected fraction = |Γ|² ML = −10 × log10 (1 − |Γ|²) dB from a meter: |Γ| = √(P reflected / P forward)

When a load does not match the line impedance (usually 50 Ω), part of the wave is reflected. The reflection coefficient |Γ| is the ratio of reflected to forward voltage. SWR is the ratio of the highest to the lowest voltage along the line: 1:1 is a perfect match and it rises without limit as the match gets worse. Return loss says the same thing in decibels: a higher number is a better match. A network analyser shows S11 as a negative number of dB (20 × log10 |S11|); that is the return loss with the sign flipped, and return loss itself is also often written with a minus sign. This page accepts either sign.

Mismatch loss is the share of the incident power that does not reach the load because it is reflected, shown here as a positive number of dB: 2:1 costs 0.51 dB (11 % reflected), 3:1 costs 1.25 dB (25 %). It is not necessarily lost: with an antenna tuner at the transmitter, the reflected power is reflected back towards the antenna, and what is then really lost depends on the cable loss, which this page does not include. The formulas also ignore cable loss between the meter and the load.

Worked example: a power meter shows 100 W forward and 4 W reflected. |Γ| = √(4 / 100) = 0.2, SWR = (1 + 0.2) / (1 − 0.2) = 1.5:1, return loss = −20 × log10 0.2 = 13.98 dB, 0.2² = 4 % of the power is reflected, and the mismatch loss is −10 × log10(1 − 0.04) = 0.18 dB.

Sources (checked 2026-10-31):

SWR from the reflection coefficient, and reflection from forward/reflected power: https://en.wikipedia.org/wiki/Standing_wave_ratio
Reflection coefficient Γ = (Z_L − Z₀) / (Z_L + Z₀): https://en.wikipedia.org/wiki/Reflection_coefficient
Return loss = −20 log10 |Γ| dB, and its sign conventions: https://en.wikipedia.org/wiki/Return_loss
S11 and input return loss: https://en.wikipedia.org/wiki/Scattering_parameters
Mismatch loss = 10 log10 (1 − |Γ|²) dB (negative; shown positive here), and re-reflection with a match at the source: https://en.wikipedia.org/wiki/Mismatch_loss