is an international system, approved by the International Standards Organization (ISO), for classifying industrial lubricants according to viscosity. Each ISO viscosity grade number designation corresponds to the mid-point of a viscosity range expressed in centistokes (cSt) at 40°C. For example, a lubricant with an ISO grade of 32 has a viscosity within the range of 28.8 — 35.2 cSt, the mid-point of which is 32.

ISO VISCOSITY CLASSIFICATION SYSTEM
ISOaViscosity	MidPoint cSta@	Viscosity RangesacSt @ 40° C
Grades	40°C	Minimum		Maximum
2	2.2	1.98		2.42
3	3.2	2.88		3.52
5	4.6	4.14		5.06
7	6.8	6.12		7.48
10	10	9.00		11.0
15	15	13.5		16.5
22	22	19.8		24.2
32	32	28.8		35.2
46	46	41.4		50.6
68	68	61.2		74.8
100	100	90.0		110
150	150	135		165
220	220	198		242
320	320	288		352
460	460	414		506
680	680	612		748
1000	1000	900		1100
1500	1500	1350		1650
Note:  From this table that the grades above 68 are multiples of 10 or 100 of the grades from 10 through 68