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 | 1,000 |
One kilogram per kilogram in every humidity ratio unit
| 1,607,860,000 | part per billion by volume (moisture) (ppbv) | |
| 1,000,000,000 | microgram per kilogram of dry air (μg/kg) | |
| 1,607,860 | part per million by volume (moisture) (ppmv) | |
| 1,000,000 | milligram per kilogram of dry air (mg/kg) | |
| 7,000 | grain per pound of dry air (gr/lb) | |
| 1,000 | gram per kilogram (g/kg) | |
| 1 | kilogram per kilogram (kg/kg)this unit | |
| 1 | pound per pound of dry air (lb/lb) |
Solvers that use humidity ratio