Physics

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Air Mixing Ratio Calculator.

Calculate water-vapour mixing ratio from vapour pressure and total pressure.

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Results update as you type.

Mixing ratio: 0.007455 kg/kg

Mixing ratio

0.007455kg/kg
Mixing ratio: 7.454682 g/kg

Mixing ratio

7.454682g/kg

Results update automatically as you type.

Use Cases

Meteorological Analysis

Meteorologists use the mixing ratio to understand humidity in the atmosphere, which is crucial for weather forecasting and climate studies.

Example: Calculate the mixing ratio for an air parcel with vapour pressure 1500 Pa and total pressure 101325 Pa.

HVAC System Design

Engineers use mixing ratio to design ventilation and air conditioning systems, ensuring proper humidity control in buildings.

Example: Determine the mixing ratio for indoor air at 25°C with vapour pressure 2000 Pa and total pressure 101325 Pa.

Frequently Asked Questions

What is the water-vapour mixing ratio?
The water-vapour mixing ratio is the mass of water vapour per unit mass of dry air. It is calculated using the vapour pressure and total pressure, typically expressed in grams of water vapour per kilogram of dry air (g/kg).
How do I use this calculator?
Enter the water-vapour pressure in Pascals (Pa) and the total pressure in Pascals (Pa). The calculator will compute the mixing ratio using the formula: mixing ratio = 0.622 * (e / (p - e)), where e is vapour pressure and p is total pressure.
What units are used for the inputs?
Both inputs must be in Pascals (Pa). Ensure you convert from other units like hPa or kPa to Pa before entering values. For example, 1 hPa = 100 Pa.

Tips & Common Mistakes

Tips

  • Ensure both pressure values are in Pascals (Pa). Convert from hPa or kPa if necessary: 1 hPa = 100 Pa, 1 kPa = 1000 Pa.
  • The total pressure should be greater than the vapour pressure. If not, the result will be negative or undefined.
  • For accurate results, use precise measurements of vapour pressure, as small errors can significantly affect the mixing ratio.
  • This calculator is for reference; for critical applications, consult standard meteorological tables or software.

Common Mistakes to Avoid

  • Forgetting to convert pressure units to Pascals before entering them, leading to incorrect results.
  • Entering the vapour pressure as a percentage or relative humidity instead of the actual vapour pressure in Pa.
  • Using total pressure that is less than or equal to vapour pressure, which is physically impossible and yields invalid results.

Last updated: August 13, 2026