Quick answer
Absolute humidity is the mass of water vapour per cubic metre of air: AH = 216.7 × e ÷ (273.15 + T), with vapour pressure e = RH × 6.112 × exp(17.62T ÷ (243.12 + T)) hPa. At 20 °C and 50% relative humidity, AH is 8.621 g/m³.
Enter the temperature and the relative humidity. The calculator returns the absolute humidity.
Related tools: Relative Humidity Calculator: Relative humidity from air temperature and dew point. Wet Bulb Temperature Calculator: Wet-bulb temperature from air temperature and relative humidity (Stull's formula). Air Density Calculator: Density of moist air from pressure, temperature and humidity.
How to use the Absolute Humidity Calculator
- Enter temperature (°C) (between -45 and 60).
- Enter relative humidity (%) (between 0 and 100).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Temperature | A number, in °C | ≥ -45, ≤ 60 |
| Relative humidity | A number, in % | ≥ 0, ≤ 100 |
Formula and method
Formula
AH = 216.7 × (RH ÷ 100 × 6.112 × exp(17.62T ÷ (243.12 + T))) ÷ (273.15 + T) g/m³
IEEE-754 double precision; shown to the decimals indicated.
Magnus saturation vapor pressure with the ideal gas law for water vapor.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Temperature = 20; Relative humidity = 50.
| Result | Value |
|---|---|
| Absolute humidity | 8.621 g/m³ |
Example 2
Inputs: Temperature = 30; Relative humidity = 80.
| Result | Value |
|---|---|
| Absolute humidity | 24.211 g/m³ |
Example 3
Inputs: Temperature = 0; Relative humidity = 100.
| Result | Value |
|---|---|
| Absolute humidity | 4.849 g/m³ |
The first line is the headline result (absolute humidity). IEEE-754 double precision; shown to the decimals indicated.
Why it differs from relative humidity
Relative humidity depends on temperature, but absolute humidity is the actual water content. At 20 °C, saturated air holds about 17.3 g/m³, so 50% RH is half of that, 8.6 g/m³.
Accuracy
The formula is approximate, accurate to about 1%. Warm air can hold more moisture, which is why heating a room lowers its relative humidity without changing the absolute humidity.
How the result changes with temperature
Holding every other input at the first worked example, this table changes only temperature. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Temperature | Absolute humidity |
|---|---|
| 10 | 4.692 g/m³ |
| 20 | 8.621 g/m³ |
| 40 | 25.491 g/m³ |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Relative humidity: entering "120" shows "Relative humidity must be at most 100." beside that field and no result.
- Temperature: left empty shows "Enter temperature." beside that field and no result.
Choosing between the Absolute Humidity Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Relative Humidity Calculator](/science/relative-humidity/) | air temperature and dew point | Relative humidity |
| [Wet Bulb Temperature Calculator](/science/wet-bulb/) | air temperature and relative humidity | Wet-bulb temperature |
| [Air Density Calculator](/science/air-density/) | pressure, temperature and relative humidity | Air density |
| [Absolute Value Calculator](/math/absolute-value-calculator/) | number | |x| |
| [Absolute Eosinophil Count Calculator](/health/eosinophil-count/) | white blood cell count and eosinophils | Absolute eosinophil count |
Background: environment and acoustics
Decibels are a logarithmic scale, so sound levels cannot be added arithmetically: two equal sources raise the level by about 3 dB, not double it. Environmental and emissions results depend on the factors behind them (for example the US EPA's equivalency factors), which are averages for a country, fuel and year.
Use the result to compare scenarios rather than as a measured value.
Assumptions and limitations
- Approximate; accurate to about 1%
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for relative humidity and temperature to confirm this.
Frequently asked questions
What is a comfortable absolute humidity?
Roughly 7 to 12 g/m³ indoors.
What is the saturation value at 30 °C?
At 30 °C saturated air holds about 30.4 g/m³, so 50% relative humidity is about 15.2 g/m³.
Why is it used?
Engineers use it to size humidifiers.
What does the Absolute Humidity Calculator calculate?
Water vapor content of air in grams per cubic meter. It returns Absolute humidity.
What formula does the Absolute Humidity Calculator use?
AH = 216.7 × (RH ÷ 100 × 6.112 × exp(17.62T ÷ (243.12 + T))) ÷ (273.15 + T) g/m³. Magnus saturation vapor pressure with the ideal gas law for water vapor.
What do I need to enter in the absolute Humidity Calculator?
You enter Temperature (°C) and Relative humidity (%).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Approximate; accurate to about 1%.
What is an example of a absolute Humidity result?
With temperature 20 and relative humidity 50, the absolute humidity is 8.621 g/m³.
Where does the method come from?
The method follows: Magnus formula as used in WMO guidance; ideal gas law.
Related calculators
- Relative Humidity Calculator — Relative humidity from air temperature and dew point.
- Wet Bulb Temperature Calculator — Wet-bulb temperature from air temperature and relative humidity (Stull's formula).
- Air Density Calculator — Density of moist air from pressure, temperature and humidity.
- Absolute Value Calculator — Absolute value of a number.
- Mean Absolute Deviation Calculator — Average distance of values from the mean.
- Sound Level Calculator — Combine decibel levels, or convert sound intensity to decibels.
- Doppler Effect Calculator — Observed frequency from source and observer speeds.
- Wavelength Calculator — Wavelength from wave speed and frequency.
Sources
- Magnus formula as used in WMO guidance; ideal gas law
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.