According to MIL-D-3464, a desiccant unit is the quantity of desiccant that will adsorb 3.00 grams of water vapor at 20%RH and 25◦C, as well as 6.00 grams at 40%RH and 25◦C. Therefore, a unit of desiccant differs depending on the type of desiccant measured. For example, one unit of silica gel is equivalent to 26 grams, while one unit of molecular sieve corresponds to 28 grams. Furthermore, a minimum of 1.2 units of desiccant per cubic foot of air volume is recommended as a general best practice.