VSWR Calculator — Voltage Standing Wave Ratio
Calculate all key RF mismatch parameters — VSWR, reflection coefficient (|Γ|), return loss, mismatch loss and reflected power percentage — by entering VSWR directly, a reflection coefficient, a return loss value or source/load impedances.
Input type
Voltage standing wave ratio — 1.0 = perfect match, > 2 = significant mismatch
- 1
Reflection coefficient |Γ|
(VSWR − 1) ÷ (VSWR + 1) = (1.5 − 1) ÷ (1.5 + 1) = 0.2 - 2
VSWR (direct input)
1.500
How does this calculator work?
VSWR = (1 + |Γ|)/(1 − |Γ|) where |Γ| = |ZL − ZS|/|ZL + ZS| is the reflection coefficient. Enter VSWR, |Γ|, return loss or impedances to get all mismatch parameters. VSWR = 1.0 is a perfect match; VSWR > 3 reflects over 25% of incident power.
Formula
How this is calculated
When an electromagnetic wave travelling on a transmission line reaches a load impedance that differs from the line's characteristic impedance (ZS), some power is reflected back towards the source. The reflection coefficient Γ quantifies this: Γ = (ZL − ZS) / (ZL + ZS). Its magnitude (|Γ|) ranges from 0 (perfect match, all power delivered) to 1 (full reflection, no power delivered). The incident and reflected waves superimpose to form a standing wave pattern along the line.
VSWR (voltage standing wave ratio) is the ratio of the voltage maximum to voltage minimum in that standing wave pattern, given by VSWR = (1 + |Γ|) / (1 − |Γ|). A perfect match gives VSWR = 1.0; in practice a VSWR below 1.5 (|Γ| ≈ 0.2) is excellent, 1.5–2.0 is acceptable for many applications, and above 3.0 the reflected power exceeds 25%.
Return loss (RL) expresses the reflected power ratio in decibels: RL = −20 log₁₀(|Γ|). Higher return loss is better (20 dB → |Γ| = 0.1 → ~1% reflected power). Mismatch loss is the dB reduction in delivered power due to the impedance mismatch.
Frequently asked questions
For most amateur and commercial antenna installations, VSWR below 1.5:1 is considered excellent, 1.5–2.0:1 is acceptable and above 3:1 signals significant mismatch that can stress transmitter finals and reduce radiated power. Some broadband designs tolerate up to 2.5:1 across the band.
Return loss (dB) = −20 log₁₀(|Γ|) = −20 log₁₀((VSWR − 1)/(VSWR + 1)). A VSWR of 1.5 corresponds to a return loss of about 14 dB; VSWR 2.0 → 9.5 dB; VSWR 3.0 → 6.0 dB. Higher return loss (larger positive number) means less reflection.
The VSWR on a lossless line is the same at every point along the line — it is determined solely by the mismatch at the load. However, on a real lossy cable, VSWR measured at the transmitter end appears lower than the actual load VSWR because the cable attenuates both forward and reflected signals.
Also known as
TG we-Calculate Editorial Team. (2026). VSWR Calculator — Voltage Standing Wave Ratio [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/vswr-voltage-standing-wave-ratio-calculator
TG we-Calculate Editorial Team. "VSWR Calculator — Voltage Standing Wave Ratio." TG we-Calculate. 2026. https://we-calculate.com/calculator/vswr-voltage-standing-wave-ratio-calculator.
TG we-Calculate Editorial Team, "VSWR Calculator — Voltage Standing Wave Ratio," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/vswr-voltage-standing-wave-ratio-calculator
@misc{wecalculate_vswr_voltage_standing_wave_ratio_calculator, title = {VSWR Calculator — Voltage Standing Wave Ratio}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/vswr-voltage-standing-wave-ratio-calculator}}, year = {2026}, note = {TG we-Calculate} }
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