Absolute Humidity Calculator
Calculate the mass of water vapor in air from temperature and relative humidity. Useful for HVAC design, weather analysis, indoor air quality checks, and comfort studies.
Enter temperature and relative humidity to calculate absolute humidity in grams per cubic meter or milligrams per cubic meter.
Absolute Humidity Calculator
Use Fahrenheit or Celsius. The slider updates with the selected unit.
Relative humidity percentage (0-100%)
Water vapor mass in air
Enter temperature and humidity, then calculate.
Absolute humidity will appear here
What Is Absolute Humidity?
Absolute humidity is the actual amount of water vapor in air, measured as mass per unit volume. Unlike relative humidity, which changes with temperature, absolute humidity tells you the real moisture content in the air. That makes it a useful metric for HVAC work, weather comparison, indoor comfort studies, and air quality analysis.
If you want to compare two spaces or two weather conditions fairly, absolute humidity is often the better number to look at. Relative humidity can be high in cool air even when the air does not hold much moisture. Absolute humidity gives you the direct moisture load.
HVAC planning
Helps estimate moisture load, comfort levels, and dehumidification needs.
Weather comparison
Makes it easier to compare humid air across different temperatures and locations.
Indoor comfort
Useful for monitoring moisture levels in bedrooms, offices, basements, and storage rooms.
How it works
The calculator estimates the saturation vapor pressure from temperature, scales it by relative humidity, and then converts that vapor pressure into mass per cubic meter.
- Input: temperature and relative humidity
- Output: grams per cubic meter or milligrams per cubic meter
- Best for: HVAC, indoor comfort, and weather analysis
Formula summary
The calculator uses the Magnus equation for vapor pressure and the standard absolute humidity relationship for moist air.
es = 6.112 x exp((17.67 x T) / (T + 243.5))e = RH / 100 x esAH = 216.7 x e / (T + 273.15)Quick Reference Values
These are approximate values calculated with the same formula used by the calculator.
| Temperature | Relative Humidity | Absolute Humidity | Condition |
|---|---|---|---|
| 20 C | 50% | 8.64 g/m3 | Comfortable |
| 25 C | 60% | 13.81 g/m3 | Warm |
| 30 C | 70% | 21.24 g/m3 | Humid |
| 35 C | 80% | 31.68 g/m3 | Very Humid |
| 0 C | 30% | 1.45 g/m3 | Cold and Dry |
| 0 C | 50% | 2.42 g/m3 | Cold Room |
| 5 C | 40% | 2.72 g/m3 | Cool and Dry |
| 5 C | 60% | 4.08 g/m3 | Damp Morning |
| 10 C | 30% | 2.82 g/m3 | Cool and Dry |
| 10 C | 50% | 4.70 g/m3 | Mild |
| 10 C | 70% | 6.57 g/m3 | Rainy Cool |
| 15 C | 40% | 5.13 g/m3 | Fresh Indoor Air |
| 15 C | 60% | 7.69 g/m3 | Comfortable |
| 18 C | 50% | 7.68 g/m3 | Typical Indoor |
| 20 C | 40% | 6.91 g/m3 | Comfortable |
| 20 C | 70% | 12.09 g/m3 | Warm Indoor |
| 25 C | 40% | 9.21 g/m3 | Warm |
| 25 C | 50% | 11.51 g/m3 | Warm and Balanced |
| 25 C | 80% | 18.42 g/m3 | Humid |
| 30 C | 40% | 12.14 g/m3 | Hot |
| 30 C | 60% | 18.21 g/m3 | Very Warm |
| 30 C | 90% | 27.31 g/m3 | Sticky |
| 35 C | 50% | 19.80 g/m3 | Hot and Humid |
| 35 C | 90% | 35.64 g/m3 | Extreme Heat |
Frequently Asked Questions
Is absolute humidity the same as relative humidity?
No. Relative humidity is a percentage of how much water vapor the air is holding compared to the maximum it could hold at that temperature. Absolute humidity is the actual mass of water vapor in the air.
Why does temperature matter?
Warmer air can hold more moisture. That means the same relative humidity percentage can represent very different actual moisture amounts at different temperatures.
When should I use absolute humidity?
Use it when you want to compare moisture content directly between rooms, cities, seasons, or HVAC conditions without the temperature percentage effect.
What output unit should I choose?
Choose g/m3 for most everyday use. Pick mg/m3 if you need a larger number for technical or scientific reporting.