Calculator for Mixing Ratio of Water Vapor and Specific Humidity

Calculates the amount of water vapor in the air from barometric pressure, temperature and relative humidity. The mixing ratio indicates how many grams of water vapor are contained in one kilogram of dry air. The specific humidity, on the other hand, is the ratio of water vapor to moist air. Please enter the air pressure in hectopascals, the temperature in degrees Celsius and the relative humidity in percent to calculate the mixing ratio and specific humidity.

Example: at an air pressure of 1024 hPa, a temperature of 20 degrees centigrade and 50 percent humidity, the mixing ratio is 7.19 grams of water vapor per kilogram of dry air and the specific humidity is 7.14 grams of water vapor per kilogram of humid air.

The calculation is carried out using Peter Mander's approximation formulas: How to calculate Mixing Ratio and Specific Humidity

The relative humidity indicates what percentage of the maximum possible water vapor is dissolved in the air. The warmer the air, the higher the mass of water vapor that can be absorbed. Therefore, at the same humidity, warm air contains a higher amount of water than cold air. When one hundred percent humidity is reached, the air can no longer absorb water as long as it does not change its temperature. When air with a high humidity cools down, part of the dissolved water vapor becomes liquid, the water condenses, and condensation, dew, fog or rain form.
The specific humidity is also known as the degree of humidity. The value of grams per kilogram is equivalent to per thousand, so in the above example the degree of humidity is about 7 per thousand or 0.7 percent. The absolute humidity refers to the mass of water vapor per cubic meter of air, it can be calculated from the specific humidity if the density of the air is known. This can be taken from according tables.

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