Meteorologists track moisture with the mixing ratio because it doesn’t change when air rises or sinks (until clouds form). It is plotted on every Skew-T diagram used in weather forecasting.
How to use the Mixing Ratio of Air Calculator
- Air temperature
- Dew point
- Air pressure
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter the air temperature, dew point and air pressure.
Inputs explained
| Field | What to enter |
|---|---|
| Air temperature | Units: °C, °F, K |
| Dew point | Units: °C, °F, K |
| Air pressure | Units: hPa, kPa, inHg, mmHg, psi, atm |
What each result means
- Vapour pressure = 6.112×exp(17.62×([Dew point])÷(243.12 + ([Dew point])))
- Saturation vapour pressure = 6.112×exp(17.62×([Air temperature])÷(243.12 + ([Air temperature])))
- Mixing ratio = 621.97×[Vapour pressure]÷([Air pressure]÷100 – [Vapour pressure])
- Saturation mixing ratio = 621.97×[Saturation vapour pressure]÷([Air pressure]÷100 – [Saturation vapour pressure])
- Relative humidity = [Vapour pressure]÷[Saturation vapour pressure]×100
Example values
How the main result changes when Air temperature changes and everything else stays at the example values above:
| Air temperature (°C) | Mixing ratio (g/kg) |
|---|---|
| 12.5 | 10.6239 |
| 18.75 | 10.6239 |
| 25 | 10.6239 |
| 31.25 | 10.6239 |
| 37.5 | 10.6239 |
| 50 | 10.6239 |
Formula
e = e_s(T_d), w = 621.97·e/(p − e) g/kg, w_s = 621.97·e_s(T)/(p − e_s(T)), RH ≈ e/e_s(T)
Worked example
Inputs — Air temperature: 25 °C; Dew point: 15 °C; Air pressure: 1,013.25 hPa.
Results — Vapour pressure = 17.01672 hPa; Saturation vapour pressure = 31.60057 hPa; Mixing ratio = 10.62391 g/kg; Saturation mixing ratio = 20.02202 g/kg; Relative humidity = 53.8494 %.
Key terms
- Mixing ratio
- Mass of water vapour per mass of dry air.
Frequently asked questions
What is a typical mixing ratio?
5–20 g/kg near the surface in mid-latitudes.
Why is it conserved?
It counts water per dry air, so expansion doesn't change it.
How does it differ from specific humidity?
Specific humidity is per kilogram of moist air.
What is the saturation mixing ratio?
The maximum mixing ratio at that temperature and pressure.