kg/kg
kilogram per kilogram
Humidity ratioexact by definition
The kilogram per kilogram is the SI form of humidity ratio, also called the mixing ratio or absolute humidity by mass: kilograms of water vapour per kilogram of DRY air. Its factor of 1 is exact. Comfortable indoor air sits around 0.008 to 0.010 kg/kg, and saturated air at 30 °C holds about 0.027.
Watch out: The denominator is dry air, not moist air. This is deliberate: the mass of dry air in a sample does not change as moisture is added or removed, so a humidity ratio expressed per kilogram of dry air stays meaningful through a humidification or dehumidification process. Every quantity on a psychrometric chart is per kilogram of dry air for the same reason.
| 1 kg/kg | 1,000 g/kg |
Solvers that use humidity ratio