Wet-bulb temperature

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Wet-bulb temperature is factor in the determination of relative humidity. Wet-bulb temperature is measured using a thermometer that has its bulb wrapped in cloth—called a sock—that is kept wet with water via wicking action. Such an instrument is called, not surprisingly, a wet-bulb thermometer. At relative humidities below 100%, water evaporates from the bulb which cools the bulb below ambient temperature. To determine relative humidity, ambient temperature is measured using an ordinary thermometer, better known in this context as a dry-bulb thermometer. At any given ambient temperature, less relative humidity results in a greater difference between the dry-bulb and wet-bulb temperatures; the wet bulb is colder. The precise relative humidity is determined by finding one's wet-bulb and dry-bulb temperatures on a lookup chart (or via complex calculation).

Hygrometers are instruments comprising both wet-bulb and dry-bulb thermometers. A hygrometer can also be used in combination with a globe thermometer (for measuring solar radiant heat) in the calculation of the wet bulb globe temperature.