Calculate humidity mixing ratio, specific humidity, absolute humidity, dew point, enthalpy, and moist air density from temperature, RH, and pressure.
The mixing ratio (or humidity ratio) is the mass of water vapor per unit mass of dry air, typically expressed in grams per kilogram. It is a fundamental quantity in atmospheric science, HVAC engineering, and meteorology because — unlike relative humidity — it doesn't change with temperature alone. Two air masses with the same mixing ratio contain the same amount of moisture regardless of temperature.
Understanding the mixing ratio is essential for weather forecasting (predicting cloud formation, precipitation), HVAC design (sizing dehumidifiers, selecting coils), and industrial processes where moisture control matters. It connects directly to dew point, enthalpy, and air density, forming the backbone of psychrometric calculations.
This calculator computes the mixing ratio along with specific humidity, absolute humidity, volume mixing ratio (ppm), dew point, enthalpy, and moist air density. Multiple temperature and pressure units are supported, with altitude-aware presets for different climates. A saturation bar shows how close the air is to condensation, and a temperature sweep table reveals how moisture capacity changes across the temperature range.
Use this calculator when you need the actual moisture content of air rather than a temperature-dependent humidity percentage, especially for HVAC sizing, psychrometrics, and weather analysis. It is a better fit when you care about conserved moisture content instead of a number that shifts with temperature. That makes it easier to compare indoor and outdoor air on the same moisture basis.
Saturation Pressure: Ps = 610.78 × exp(17.27T / (T + 237.3)) Pa Mixing Ratio: W = 0.622 × Pv / (P − Pv) kg/kg Specific Humidity: q = W / (1 + W) Absolute Humidity: ρv = Pv / (Rv × T) Volume Mixing Ratio: χ = Pv / P Enthalpy: h = 1.006T + W(2501 + 1.86T) kJ/kg Dew Point: Td = 237.3 × α / (17.27 − α)
Result: W = 9.88 g/kg, Ws = 19.77 g/kg, Td = 13.9°C
At 25°C and 50% RH, each kilogram of dry air holds 9.88 g of water vapor. The air could hold up to 19.77 g/kg at saturation. Cooling below 13.9°C will cause condensation.
Relative humidity is useful for comfort discussions, but it changes as air warms or cools even when no moisture is added or removed. Mixing ratio tracks the actual mass of water vapor carried by the air, which is why meteorologists and HVAC engineers use it for process and weather calculations.
When comparing indoor and outdoor air streams, look at dew point and enthalpy alongside mixing ratio. That combination tells you whether latent load or sensible load is driving equipment selection. It also helps explain why two spaces can share the same temperature but feel very different.
Do not mix up absolute humidity, specific humidity, and mixing ratio. They are related, but they are not interchangeable in design calculations. Pressure assumptions also matter at altitude, so use the local atmospheric pressure when you are not working near sea level.
Mixing ratio is vapor mass per dry air mass (W). Specific humidity is vapor mass per total moist air mass (q = W/(1+W)). They are nearly identical at low humidity levels.
RH changes with temperature even if no moisture is added or removed. Mixing ratio is conserved during adiabatic processes, making it more useful for tracking actual moisture.
The mass of water vapor per unit volume of air (g/m³). Unlike mixing ratio, it depends on both temperature and pressure.
The dew point is the temperature at which the current water-vapor content exactly reaches saturation. Cooling below that temperature causes condensation to begin.
Water vapor has a lower molecular mass than the nitrogen and oxygen it displaces, so humid air can be less dense than dry air at the same temperature and pressure. That density difference is why humid air can slightly reduce lift and change ventilation behavior.
Yes. At lower atmospheric pressure, the same relative humidity corresponds to a slightly different vapor-pressure balance, which shifts the resulting mixing ratio.