SAE J300

SAE J300 is a standard that defines the viscometric properties of mono- and multigrade engine oils, maintained by SAE International. Key parameters for engine oil viscometrics are the oil's kinematic viscosity, its high temperature-high shear viscosity measured by the tapered bearing simulator, and low temperature properties measured by the cold-cranking simulator and mini-rotary viscometer. This standard is commonly used throughout the world, and standards organizations that do so include API and ILSAC, and ACEA.
Viscosity grades.
SAE viscosity grades include 0W through 25W in increments of 5W, 8 through 20 in increments of 4, and 20 through 60 in increments of 10. The former grades denote a multigrade engine oil's low-temperature properties (W denoting "winter"), whereas the latter grades denote an engine oil's properties at the operating temperature of an engine. To illustrate, a lawnmower may require SAE 30 monograde engine oil that must meet the SAE 30 requirements. In comparison, a contemporary passenger car engine may require SAE 0W-20 multigrade engine oil that must meet both the SAE 0W and SAE 20 requirements. 
The addition of the SAE 8 through SAE 16 viscosity grades permit improved fuel economy through reduced hydrodynamic friction.