Humidity Calculator.

Convert between relative humidity, absolute humidity, specific humidity, dew point and vapor pressure. Enter temperature and any one humidity measure.

How to convert humidity measures

  1. Enter the air temperature.
  2. Enter the humidity figure you already have — relative, absolute or dew point.
  3. Read the other measures, all computed from the same saturation vapour pressure.
  4. Use absolute humidity when you care about the actual water content, relative humidity when you care about how it feels.

Humidity Types Explained

Relative Humidity (%)

The ratio of actual water vapor present to the maximum possible at the current temperature, expressed as a percentage. It changes when temperature changes, even if the moisture content stays the same.

Absolute Humidity (g/m³)

The actual mass of water vapor in a given volume of air. Unlike relative humidity, it does not change with temperature — only with the actual amount of moisture in the air.

Specific Humidity (g/kg)

The ratio of water vapor mass to the total mass of moist air. Commonly used in meteorology and HVAC engineering. More useful than absolute humidity for air-mass analysis.

Frequently Asked Questions

What is the difference between relative and absolute humidity?

Absolute humidity is the mass of water vapour in a cubic metre of air (g/m³). Relative humidity is how much vapour the air holds as a percentage of the most it could hold at that temperature. Air at 25 °C and 50% RH holds about 11.5 g/m³.

What is specific humidity?

Specific humidity is the mass of water vapour per kilogram of air (g/kg). Unlike relative humidity it does not change when air warms or cools without gaining or losing moisture, which makes it the quantity meteorologists track. Air at 25 °C and 50% RH has about 9.8 g/kg.

What is a comfortable indoor humidity?

Most guidance puts it between 40% and 60% relative humidity. Below about 30% skin and airways dry out; above about 60% mould and dust mites thrive. At 20 °C, 50% RH corresponds to a dew point of about 9 °C.

Why does relative humidity rise at night?

Because the air cools while the amount of water vapour in it stays the same. Colder air can hold less vapour, so the same moisture is a larger share of the maximum. When the air cools to its dew point, relative humidity reaches 100% and dew forms.

Sources · Reviewed

  • Alduchov OA, Eskridge RE (1996), improved Magnus form, J Appl Meteorol 35:601–609

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