...
All gridded data is made available in Decimal Degrees, lat/lon, with latitude values in the range [-90;+90] referenced to the equator and longitude [-180;180values in the range [0;360] referenced to the Greenwich Prime Meridian. Some software applications automatically display longitudes in the range [-180;+180].
Earth model
For data in GRIB1 format the earth model is a sphere with radius = 6367.47 km, as defined in the WMO GRIB Edition 1 specifications, Table 7, GDS Octet 17
...