Enter humidity and atmospheric values
Chemistry and psychrometric equations
1) Saturation vapor pressure
es = 0.61078 × exp[(17.2694 × T) / (T + 237.3)]
T is air temperature in Celsius, and es is in kPa.
2) Actual vapor pressure
e = (RH / 100) × es
RH is relative humidity expressed as a percent.
3) Mixing ratio
w = 0.62198 × e / (P − e)
P is total atmospheric pressure in kPa. The result is kilograms of water vapor per kilogram of dry air.
4) Specific humidity
q = w / (1 + w)
This converts the humidity ratio into total moist-air mass fraction.
Steps for reliable results
- Enter the measured air temperature.
- Select the matching temperature unit.
- Enter relative humidity as a percentage.
- Enter atmospheric pressure and choose its unit.
- Select the desired output unit for mixing ratio.
- Choose decimal precision and graph sample points.
- Click the calculate button.
- Review the result block above the form, graph, and export options.
Sample chemistry and air-moisture cases
| Case | Temperature | Relative Humidity | Pressure | Mixing Ratio |
|---|---|---|---|---|
| Cool indoor air | 20 °C | 50% | 101.325 kPa | 7.26 g/kg dry air |
| Warm humid lab | 30 °C | 60% | 101.325 kPa | 16.07 g/kg dry air |
| Cool damp morning | 10 °C | 80% | 101.325 kPa | 6.09 g/kg dry air |
Frequently asked questions
1) What does mixing ratio mean?
Mixing ratio is the mass of water vapor divided by the mass of dry air. It helps compare moisture content directly, regardless of the current volume of the air sample.
2) Is mixing ratio the same as relative humidity?
No. Relative humidity compares actual vapor pressure to saturation vapor pressure. Mixing ratio measures actual water vapor mass relative to dry air mass.
3) Why is pressure included?
Pressure changes the relationship between vapor pressure and humidity ratio. The same temperature and humidity can produce slightly different mixing ratios at different atmospheric pressures.
4) Which temperature range works best?
This page works well for ordinary atmospheric and classroom calculations. Very extreme temperatures may need specialized equations for higher scientific accuracy.
5) What output unit should I choose?
Use g/kg dry air for everyday interpretation. Use kg/kg dry air for strict thermodynamic work. Use lb/lb dry air for some engineering references.
6) What is humidity ratio deficit?
It is the difference between the saturation mixing ratio and the actual mixing ratio. It shows how much more moisture the air could hold before reaching saturation.
7) Why does the graph curve upward?
Mixing ratio rises with relative humidity, but the relationship is not perfectly linear because the equation depends on vapor pressure and total pressure together.
8) Can I use this for weather and chemistry study?
Yes. It is useful for basic atmospheric chemistry, moisture calculations, psychrometric practice, classroom exercises, and quick weather-related estimation.