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How to Calculate Moisture Content at Saturation

Water vapor density or moisture content measures the weight of water vapor contained in a given amount of air. Saturation occurs when the air cannot hold additional water vapor. The temperature of the air will dictate the maximum amount of water vapor possible, or the saturation point. This temperature, at which water vapor must begin to condense into liquid, is called the dew point. Moisture content at saturation can be calculated by first finding the moisture pressure.

Things You'll Need

Scientific calculator
Thermometer

Instructions

- 1
  Determine the temperature of the saturated air.
- 2
  Convert the temperature from Fahrenheit to Celsius. To do this, multiple the temperature by 32. Multiply the product by 5/9.
- 3
  Convert the temperature from Celsius to Kelvins by adding 273.16 to the Celsius value.
- 4
  Calculate the saturation pressure of the water vapor. The equation for this is, e^(77.3450 + 0.0057 * K - 7235 / K)) / K^8.2, where K is the temperature in Kelvins. To perform this calculation, divide 7235 by the Kelvin temperature, and subtract this from the product of the Kelvin temperature times 0.0057. Add 77.3450 to the value you obtained. Raise the exponential constant, 2.71828, to the power of the previous value. Divide the number you obtain by the Kelvin temperature raised to the power of 8.2.
- 5
  Calculate the moisture content of saturated air. The equation is, (0.0022 * Pw) / K, where Pw is the saturation pressure you previously calculated, and K is the temperature in Kelvins. To perform this calculation, divide the product of the saturation pressure times 0.0022, by the temperature in Kelvins. This number is the moisture content in kilograms per square meter of saturated air.
- 6
  Multiply the moisture content by 1000 to obtain grams of water vapor per square meter.

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