Aviowiki mostly uses the International System of Units for data served via the API.
The main deviation from this is the use of Celsius Degrees in place of Kelvin, for temperatures. This minor variation reflects the more operational use of our data, as compared to the scientific focus of the ISU.
As a general overview, these are the units of measurement used for different use cases:
Length and Altitude: meters
Temperature: Celsius degrees
Coordinates: decimal degrees
For full details about the format of each field, refer to the definition in the relevant data model.