What is the mixing ratio?

The mixing ratio (w) is the mass of water vapor per unit mass of dry air, expressed in grams per kilogram (g/kg). It is conserved during adiabatic processes, making it useful in atmospheric science.

How is mixing ratio different from specific humidity?

Specific humidity (q) is the mass of water vapor per unit mass of moist air (dry air plus vapor), while mixing ratio divides by dry air mass only. The two values are very close but not identical. Specific humidity is always slightly smaller.

What formula is used for saturation vapor pressure?

This calculator uses the Magnus formula: es = 6.1078 * exp(17.27 * T / (T + 237.3)) hPa, where T is temperature in Celsius. It is accurate to within 0.1% over the range -40 C to 60 C.

Why does atmospheric pressure matter?

The mixing ratio depends on the ratio of vapor pressure to total pressure. At higher altitudes where pressure is lower, the same vapor pressure yields a higher mixing ratio. The default pressure of 1013.25 hPa corresponds to sea level.

What is absolute humidity?

Absolute humidity is the mass of water vapor per unit volume of air, in grams per cubic meter (g/m3). Unlike mixing ratio, it changes with temperature and pressure even if the amount of vapor stays constant.

Is this the same as a paint or dilution mixing ratio?

No. This tool computes the meteorological mixing ratio — the mass of water vapor per kilogram of dry air. To mix two-part products or dilute a concentrate by a ratio such as 5:1, use a dilution ratio calculator instead.

Mixing Ratio Calculator

Name: Mixing Ratio Calculator
Availability: InStock
Author: Nham Vu

Calculate water vapor mixing ratio, specific humidity, absolute humidity, and vapor pressure from temperature, relative humidity, and atmospheric pressure.

Input Parameters

Temperature

Relative Humidity (%)

60%

Atmospheric Pressure (hPa)

Sea level standard = 1013.25 hPa

Mixing Ratio

—

g/kg of dry air

w = 0.622 × e / (p − e)

Specific Humidity

—

g/kg of moist air

q = w / (1 + w/1000)

Absolute Humidity

—

g/m³

ρ_v = 216.7 × e / T_K

Vapor Pressure

—

hPa (actual)

e = RH/100 × e_s(T)

Summary

Calculate water vapor mixing ratio, specific humidity, absolute humidity, and vapor pressure from temperature, relative humidity, and atmospheric pressure.

How it works

Enter the air temperature, relative humidity, and atmospheric pressure.
Saturation vapor pressure (es) is computed from temperature using the Magnus formula.
Actual vapor pressure (e) is found by multiplying es by the relative humidity.
The mixing ratio is calculated with w = 0.622 × e / (p − e), in grams per kilogram.
Specific humidity and absolute humidity are derived from the same vapor pressure.

Use cases

Meteorology and weather analysis requiring precise humidity metrics.
HVAC engineering to size humidification and dehumidification systems.
Agricultural science to assess crop evapotranspiration conditions.
Aviation pre-flight density altitude and engine performance checks.
Climate research comparing humidity across different pressure levels.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu