Virtual Temperature Calculator

Moist air is less dense than dry air because water vapor molecules (molecular weight approximately 18 g/mol) are lighter than the average molecular weight of dry air (approximately 28.97 g/mol). The calculator uses multiple methods depending on your available inputs. Using actual vapor pressure and station pressure, the formula is expressed as T_v = T / (1 - 0.379 * (e / P)), where T is the ambient temperature in Kelvin, e is the actual vapor pressure, and P is the station pressure. Alternatively, when utilizing the mixing ratio, the formulation is T_v = T * (1 + 0.00061 * r), where r is the mixing ratio in grams per kilogram.

Let us calculate the virtual temperature of moist air given an ambient temperature of 20 °C (293.15 K) and a mixing ratio of 6.70 g/kg. First, convert the ambient temperature into Kelvin if necessary, or use the mixing ratio formula directly. Using the mixing ratio method: T_v = 293.15 * (1 + 0.00061 * 6.70). Multiplying the mixing ratio factor gives 0.00061 * 6.70 = 0.004087. Adding one yields 1.004087. Finally, multiplying by the ambient temperature gives 293.15 * 1.004087 = 294.35 K, which is approximately 21.2 °C. This shows how moisture increases the effective temperature of the air parcel regarding buoyancy.

Always ensure that your temperature inputs are converted to absolute temperature units like Kelvin when dealing with pressure-based formulas, as mixing absolute scales prevents severe mathematical errors. Pay close attention to your units for vapor pressure and station pressure; they must be expressed in the same units—typically hectopascals (hPa) or millibars (mb)—so that they cancel out correctly in the ratio.