SWR calculator
Standing wave ratio from forward and reflected power. Shows return loss, mismatch loss, and reflected percentage.
What SWR tells you
SWR measures how well your antenna system's impedance matches your transmitter's output (usually 50 ohms). A perfect match is 1:1. In practice, anything under 1.5:1 is excellent and under 2:1 is fine for most operating.
The number people fixate on is the SWR ratio itself, but the more useful number is the mismatch loss in dB. At 2:1 SWR, you're losing about 0.5 dB to mismatch, which is less than the loss in 10 meters of RG-58 coax at VHF. At 3:1, loss is about 1.25 dB. The coax between your radio and antenna usually wastes more power than a moderate SWR mismatch does.
Why your radio cares anyway
Modern transceivers have SWR protection circuits that reduce output power when SWR climbs above 2:1 or 3:1. The radio is protecting its final amplifier transistors from reflected energy, not worrying about your efficiency. So even though 3:1 only wastes about 25% of your power to reflection, your radio may be cutting its output by 50% or more in response.