How this calculator works
Virtual temperature is the temperature dry air would need to have the same density as a moist sample at the same total pressure. It uses absolute temperature and the gas molecular-mass ratio. Mixing-ratio mode needs no pressure; dew-point and vapour-pressure methods require total absolute pressure. Reverse modes infer moisture from the virtual-to-actual temperature ratio. Condensed liquid and ice are excluded. Without a known pressure, the mixing-ratio method cannot check saturation, so very large ratios may describe a supersaturated ideal mixture outside normal weather conditions.
Formula
Tv = T(1+w/epsilon)/(1+w) = T/[1-(1-epsilon)e/p], epsilon = 0.621945. w = epsilon e/(p-e).
Worked example
Dry air has w = 0, so a 300 K sample has virtual temperature 300 K. Adding vapour at unchanged actual temperature raises virtual temperature.
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Frequently asked questions
Why must I use kelvins in the formula?
The equation compares ratios of absolute temperatures. Celsius zero is arbitrary and cannot be used in those ratios.
Is virtual temperature a thermometer reading?
No. It is a density-equivalent quantity computed from actual temperature and composition.
Can I recover pressure from a dry sample?
No. If Tv equals T, the moisture correction vanishes and pressure is undetermined by these temperatures.