Dry-bulb temperature (Tdb, DBT or Td), is a measure of air temperature. It is referred to as dry-bulb temperature because the thermometer bulb is dry and so the temperature recorded does not vary with the moisture content of the air. This is as opposed to wet-bulb temperature which is the temperature recorded by a thermometer that has its bulb wrapped in cloth and moistened with distilled water. Wet-bulb temperatures are the same as dry-bulb temperatures at a relative humidity of 100%, but otherwise wet-bulb temperatures will be lower than dry-bulb temperatures due to the cooling effect of evaporation (described as wet-bulb depression).
A sling psychrometer holds both wet and dry-bulb thermometers and can be used to express the physical and thermal properties of moist air on a psychrometric chart.
Dry-bulb temperature can be measured by a thermometer exposed to the air but shielded from radiation and moisture. It can be expressed in Celsius (C), Fahrenheit (F) or Kelvin (K).
Dry-bulb temperature can be used as to express a component of thermal comfort. For example, the wet bulb globe temperature index (WBGT) is widely used for the assessment of heat stress and combines wet-bulb temperature, dry-bulb temperature and globe temperature (mean radiant temperature).
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