Altitude Temperature Calculator
Calculate temperature at any altitude using ISA lapse rate. Find atmospheric pressure, air density, and boiling point changes for aviation and mountaineering.
Absolute Humidity Calculator
Calculate absolute humidity from temperature and relative humidity. Find moisture content in grams per cubic meter for HVAC, weather, and climate analysis.
°C
%
m
Standard: 1013.25 hPa
hPa
Absolute Humidity⧉
11.51 g/m³
Mass of water vapor per cubic meter of air
Saturation AH⧉
23.02 g/m³
Maximum possible moisture at this temperature
Moisture Deficit⧉
11.51 g/m³
Additional moisture air can hold before saturation
Dew Point⧉
13.5 °C
Temperature at which condensation begins
Mixing Ratio⧉
9.88 g/kg
Grams of vapor per kg of dry air
Specific Humidity⧉
9.78 g/kg
Grams of vapor per kg of moist air
Comfort Level⧉
Comfortable
Based on absolute humidity ranges
Vapor Pressure⧉
15.84 hPa
Partial pressure of water vapor in air
Humidity Bar
50.0%
| Temperature (°C) | Saturation AH (g/m³) | At 50% RH |
|---|---|---|
| -10 | 2.36 | 1.18 |
| 0 | 4.85 | 2.43 |
| 10 | 9.40 | 4.70 |
| 20 | 17.30 | 8.65 |
| 25 | 23.05 | 11.53 |
| 30 | 30.38 | 15.19 |
| 35 | 39.63 | 19.82 |
| 40 | 51.19 | 25.60 |
Planning notes, formulas, and examples
About the Absolute Humidity Calculator
The **Absolute Humidity Calculator** converts relative humidity and temperature readings into absolute humidity — the actual mass of water vapor present in a given volume of air, expressed in grams per cubic meter (g/m³). Unlike relative humidity, which depends on temperature, absolute humidity gives a direct, temperature-independent measure of moisture content.
Understanding absolute humidity is critical for HVAC engineers sizing dehumidification systems, meteorologists tracking moisture transport in the atmosphere, food scientists controlling storage environments, and building scientists diagnosing condensation risks. A room at 25°C and 50% RH contains roughly 11.5 g/m³ of water vapor, while the same relative humidity at 35°C yields nearly 20 g/m³ — almost double the moisture load.
This calculator also computes dew point, mixing ratio, specific humidity, and moisture deficit — providing a comprehensive picture of atmospheric moisture conditions. Enter your temperature, relative humidity, and altitude to review the moisture profile with comfort-level assessment and reference tables for quick comparison.
When This Page Helps
This calculator saves time converting between humidity metrics for HVAC design, weather analysis, indoor climate control, and food storage. Instead of looking up psychrometric charts or running manual formulas, it works through the humidity values with altitude correction.
Whether you are sizing a dehumidifier, evaluating condensation risk on cold surfaces, or analyzing weather data, the absolute humidity calculator provides the direct moisture measurement you need with supporting metrics like dew point and mixing ratio.
How to Use the Inputs
- Enter the air temperature in Celsius, Fahrenheit, or Kelvin.
- Input the relative humidity as a percentage (0-100%).
- Optionally set altitude and atmospheric pressure for altitude-corrected results.
- Use preset buttons for common scenarios (tropical, desert, winter indoor, etc.).
- Read absolute humidity, dew point, mixing ratio, and comfort level from the output cards.
- Review the reference table to compare moisture at different temperatures.
- Check the humidity bar for a visual representation of saturation level.
Formula used
Absolute Humidity (AH) = (e × 100) / (Rᵥ × T) × 1000
Where:
- e = actual vapor pressure = saturated vapor pressure × (RH / 100)
- Saturated vapor pressure: es = 6.1078 × 10^(7.5T / (237.3 + T)) (hPa, Magnus formula)
- Rᵥ = specific gas constant for water vapor = 461.5 J/(kg·K)
- T = temperature in Kelvin
- RH = relative humidity (%)Example Calculation
Result: 11.51 g/m³
At 25°C and 50% RH, the saturated vapor pressure is ~31.7 hPa, giving an actual vapor pressure of ~15.8 hPa. The absolute humidity is 15.8 × 100 / (461.5 × 298.15) × 1000 ≈ 11.51 g/m³.
Tips & Best Practices
- Use absolute humidity instead of RH when comparing moisture across different temperatures.
- Monitor dew point to predict condensation on cold surfaces like windows or pipes.
- For HVAC sizing, use the moisture deficit value to estimate dehumidification load.
- Altitude correction matters above ~1000 m — always enter altitude for mountain locations.
- Mixing ratio is preferred in meteorology because it stays constant as air rises and cools.
- Indoor comfort is typically 8-12 g/m³ — adjust humidifiers accordingly.
Understanding Absolute Humidity
Absolute humidity (AH) measures the actual water vapor mass in a given volume of air, typically expressed in grams per cubic meter (g/m³). Unlike relative humidity, which is a percentage that varies with temperature, absolute humidity provides a direct, comparable measurement.
The relationship between temperature and moisture capacity is exponential — warm air can hold dramatically more water vapor than cold air. At 40°C, saturated air contains over 51 g/m³ of moisture, while at 0°C it holds only about 4.8 g/m³. This is why winter air feels dry even at 100% RH — there simply is not much moisture present.
Applications in Engineering and Science
**HVAC Engineering:** Absolute humidity is essential for sizing dehumidification and humidification systems. A dehumidifier needs to remove a specific mass of water per hour — this is directly calculated from absolute humidity differences between indoor and target conditions.
**Building Science:** Condensation occurs when warm, moist air contacts a surface below the dew point. By knowing the absolute humidity, engineers can predict exactly where moisture problems will develop in wall assemblies.
**Food Storage:** Many foods have specific moisture tolerances. Absolute humidity monitoring ensures storage conditions remain within safe limits regardless of temperature fluctuations.
Comfort and Health Implications
Research shows that absolute humidity strongly influences respiratory health. Studies have found that influenza transmission drops significantly when absolute humidity exceeds 10 g/m³, helping explain seasonal flu patterns. Very dry air (below 5 g/m³) causes skin irritation, respiratory discomfort, and increased static electricity, while excessively humid air (above 20 g/m³) promotes mold growth and feels oppressive.
For optimal comfort and health, most building scientists recommend maintaining indoor absolute humidity between 8-12 g/m³, which corresponds roughly to 40-60% RH at typical room temperatures.
Sources & Methodology
Last updated:
Frequently Asked Questions
Relative humidity expresses moisture as a percentage of what air can hold at that temperature. Absolute humidity gives the actual mass of water vapor per unit volume (g/m³), independent of temperature.
HVAC systems must remove or add specific amounts of moisture. Absolute humidity tells engineers the actual water load, not just a percentage that changes with temperature.
Generally 8-14 g/m³ is comfortable. Below 5 g/m³ feels dry (skin irritation, static), above 20 g/m³ feels oppressively humid.
At higher altitudes, atmospheric pressure is lower, slightly affecting the calculation. Our calculator adjusts for this using the barometric formula.
Dew point is the temperature at which air becomes saturated (100% RH). When air temperature drops to the dew point, condensation occurs. Absolute humidity and dew point both measure moisture but in different ways.
In normal conditions, no — excess moisture condenses as fog or dew. However, supersaturation can briefly occur in clean air lacking condensation nuclei.
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