Umidade Absoluta
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
kg/m³
About this calculator
The Absolute Humidity calculator determines the mass of water vapor present in a volume of air, expressed in kg/m³. Unlike relative humidity, which depends on temperature, absolute humidity is a direct measure of vapor concentration. The calculation is done by dividing the mass of vapor (mv) by the volume of air (V), resulting in kg/m³. This tool is useful for engineers, HVAC technicians, and professionals working with humidity control in industrial processes.
To use the calculator, enter the mass of water vapor (in kg) and the volume of air (in m³). The result shows how many kilograms of vapor exist per cubic meter of air. This value is fundamental in air conditioning systems, industrial drying, agricultural greenhouses, and meteorology. Knowing absolute humidity helps size dehumidification equipment, predict condensation, and ensure proper conditions for storing moisture-sensitive materials.
The formula AH = mv/V is simple, but its application requires care. The mass of vapor can be obtained indirectly from relative humidity and temperature using psychrometric charts. The air volume must be measured under the same temperature and pressure conditions. In environments with temperature variations, absolute humidity remains constant if no vapor is added or removed, unlike relative humidity. This makes it a stable metric for drying and HVAC processes.
Cautions: ensure mass and volume are in the same units (kg and m³). In practical applications, direct measurement of vapor mass is difficult; it is usually calculated from vapor pressure and temperature. The calculator assumes dry air as reference, ignoring compressibility effects. For high accuracy, use updated psychrometric data. This tool is educational and aids understanding of moist air thermodynamics.
Frequently asked questions
What is the difference between absolute humidity and relative humidity?
Absolute humidity measures the mass of water vapor per volume of air (kg/m³), while relative humidity is the percentage of actual vapor pressure relative to saturation pressure at the same temperature.
How do I obtain the mass of water vapor to use in the calculator?
The vapor mass can be calculated from relative humidity and temperature using the Clausius-Clapeyron equation or psychrometric charts. Alternatively, use humidity sensors that provide mass directly.
Does the calculator work for any temperature and pressure?
Yes, as long as mass and volume values are measured under the same conditions. The formula is universal but assumes ideal behavior. For very high pressures or extreme temperatures, corrections may be needed.
Why is absolute humidity important in air conditioning systems?
It determines the vapor load that the system must remove. Dehumidification and cooling designs rely on absolute humidity to size coils and control the dew point.
Can I use this calculator for compressed air?
Yes, but note that the volume of compressed air is smaller than atmospheric volume. Use the actual volume at the system's pressure and temperature conditions.