Case 1
- Air temperature
- 25°C
- Relative humidity
- 60%
13.815g/m³
Open with these valuesAbsolute Humidity Calculator
13.815g/m³
Result: 13.815 g/m³Relative humidity alone says nothing about how much water the air holds: 80 % at 30 °C carries almost three times the water of 80 % at 10 °C. Enter temperature and relative humidity and read the vapour in grams per cubic metre — the number behind drying, storage and condensation.
The numbers at a glance
Held fixed: Air temperature 25.0 °C.
| Relative humidity (%) | Result (g/m³) |
|---|---|
| 40.0 | 9.210 |
| 50.0 | 11.513 |
| 60.0Your value | 13.815 |
| 70.0 | 16.118 |
| 80.0 | 18.420 |
Worked examples
Case 2
- Air temperature
- 10°C
- Relative humidity
- 90%
8.454g/m³
Open with these valuesCase 3
- Air temperature
- 35°C
- Relative humidity
- 40%
15.843g/m³
Open with these valuesHow it's calculated
AH = 2.1674 × 6.112 × e^(17.67·T ÷ (T + 243.5)) × RH ÷ (273.15 + T)
- StepEnter the air temperature in degrees Celsius.
- StepEnter the relative humidity as a percentage.
- StepRead the water vapour in grams per cubic metre.
- ResultWarm air carries far more water than cold air at the same percentage.
Reference table
| Temperature, humidity | Air | Water vapour |
|---|---|---|
| -10, 80 | Winter frost | 1.890 |
| 0, 100 | Freezing fog | 4.850 |
| 10, 90 | Cool and damp | 8.454 |
| 20, 50 | Living room | 8.639 |
| 25, 60 | Warm summer day | 13.815 |
| 30, 80 | Tropical | 24.283 |
| 35, 40 | Hot and dry | 15.843 |
Questions
What is absolute humidity?
The mass of water vapour in one cubic metre of air, given in grams. Unlike relative humidity it does not change when the air is heated or cooled, as long as no water is added or removed.
Why is 90 % at 10 °C drier than 50 % at 20 °C?
Because relative humidity is measured against what the air could hold at that temperature, and cold air can hold very little. The table shows both cases at roughly 8.5 grams per cubic metre.
Does the air pressure matter?
Only slightly, and this formula ignores it. Water vapour follows its own partial pressure, so the result holds at sea level and on a mountain alike.
How accurate is the result?
The Magnus approximation behind the saturation pressure is good to about 0.3 % between -40 °C and 50 °C. That is far finer than a household hygrometer, which typically reads within 3 % of relative humidity.
How much water is in a room?
Multiply the result by the room volume in cubic metres. A room of 50 cubic metres at 25 °C and 60 % relative humidity holds about 690 grams of water vapour.
Sources and last check
Information, not professional advice.