Absolute Humidity Calculator

Enter your air temperature and relative humidity to calculate the absolute humidity — the actual mass of water vapor per cubic meter of air (g/m³). You can also input atmospheric pressure for a more precise result. The Absolute Humidity Calculator returns absolute humidity in g/m³, the saturation vapor pressure, and the actual vapor pressure.

°C

Enter the air temperature in degrees Celsius.

%

Enter the relative humidity as a percentage (0–100%).

kPa

Standard sea-level pressure is 101.325 kPa. Adjust for altitude if needed.

Results

Absolute Humidity

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Saturation Vapor Pressure

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Actual Vapor Pressure

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Dew Point

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Specific Humidity (g/kg dry air)

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Vapor Pressure Breakdown

Frequently Asked Questions

What is absolute humidity?

Absolute humidity is the mass of water vapor present in a given volume of air, typically expressed in grams per cubic meter (g/m³). Unlike relative humidity, it is not dependent on temperature — it directly tells you how much water vapor is physically in the air.

How do I calculate absolute humidity from relative humidity and temperature?

First, calculate the saturation vapor pressure (Ps) using the Magnus formula based on temperature. Then multiply by relative humidity (RH/100) to get the actual vapor pressure (Pa). Finally, use the ideal gas law for water vapor: AH = (Pa × Mw) / (R × T), where Mw is the molar mass of water (18.015 g/mol), R is the gas constant (8.314 J/mol·K), and T is temperature in Kelvin.

What is the unit of absolute humidity?

The most common unit is grams of water vapor per cubic meter of air (g/m³). In some industrial applications, it may also be expressed as grams per kilogram of dry air (g/kg) or grains per pound of dry air (gr/lb).

What is the difference between absolute humidity and relative humidity?

Relative humidity (%) tells you how close the air is to being saturated with water vapor — it changes with temperature even if the actual moisture content stays the same. Absolute humidity (g/m³) tells you the actual amount of water vapor in the air, regardless of temperature or saturation level.

How does temperature affect absolute humidity?

Warmer air can hold more water vapor, so at higher temperatures the saturation vapor pressure increases. If you heat air without adding moisture, the relative humidity drops but the absolute humidity stays the same. At higher temperatures with the same relative humidity, absolute humidity is significantly greater.

What does 40% relative humidity mean?

40% relative humidity means the air contains 40% of the maximum amount of water vapor it could hold at that temperature. The actual water vapor content (absolute humidity) depends on both the temperature and this 40% figure.

How do I calculate absolute humidity from vapor pressure?

If you know the actual vapor pressure (Pa in kPa), use the formula: AH = (Pa × 1000 × 18.015) / (8.314 × T), where T is the air temperature in Kelvin. This gives you absolute humidity in g/m³.

Does atmospheric pressure affect absolute humidity?

Yes. At higher atmospheric pressures, air is denser and can contain more water vapor per cubic meter. This calculator uses your entered atmospheric pressure to refine the specific humidity calculation, making results more accurate at altitude or high-pressure conditions.

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