This gradation system, established by the Society of Automotive Engineers, has been put in place for classifying crankcase, transmission, and differential lubricants according to their viscosities. SAE numbers are used in connection with recommendations for crankcase oils to meet various design, service and temperature requirements affecting viscosity only; they do not denote quality.
Take note that a “W” grade (winter grade) indicates testing at a colder temperature. This is important in cold climates since it will take longer for the oil to warm and flow free throughout the engine. A lower “W” viscosity rating results in less engine wear because the oil can run quicker through the engine.
A viscometer is used to determine the viscosity of engine oil. Higher viscosity numbers indicate thicker oils because they take longer to flow through the viscometer when tested. It is rare that an oil will fall into one viscosity range, so centistokes (cSt) are taken into account, which more accurately show oil viscosity.
Cp, or Cloud Point, is the temperature at which paraffin wax or the solid substances begin to crystallize or separate from the solution, imparting a cloudy appearance to the oils when chilled.
Use the chart below to view what measurements determine a certain SAE grade.
| SAE VISCOSItY GRADE |
MAX CRANKING VISCOSITY (cP) |
MAX PUMPING VISCOSITY (Cp) |
MIN KINEMATIC VISCOSITY AT 100°C (cSt) |
MAX KINEMATIC VISCOSITY AT 100°C (cSt) |
HIGH TEMPERATURE HIGH SHEAR VISCOSITY (CP) |
|
0W
|
6,200 at -35°C |
60,000 at -
40°C |
3.8 |
- |
3.5 |
| 5W |
6,600 at -30°C |
60,000 at -
35°C |
3.8 |
- |
3.5 |
| 10W |
7,000 at -25°C |
60,000 at -
30°C |
4.1 |
- |
3.5 |
| 15W |
7,000 at -20°C |
60,000 at -
25°C |
5.6 |
- |
3.7 |
| 20W |
9,500 at -15°C |
60,000 at -
20°C |
5.6 |
- |
3.7 |
| 25W |
13,000 at -
10°C |
60,000 at -
15°C |
9.3 |
- |
3.7 |
| 8 |
- |
- |
4.0 |
< 6.1 |
1.7 |
| 12 |
- |
- |
5.0 |
< 7.1 |
2.0 |
| 16 |
- |
- |
6.1 |
< 8.2 |
2.3 |
| 20 |
- |
- |
6.9 |
< 9.3 |
2.6 |
| 30 |
- |
- |
9.3 |
< 12.5 |
2.9 |
| 40 |
- |
- |
12.5 |
< 16.3 |
3.7 |
| 50 |
- |
- |
16.3 |
< 21.9 |
- |
| 60 |
- |
- |
21.9 |
< 26.1 |
- |
In addition to determining what qualifies an oil for a certain SAE grade, it may be required to find equivalents of an SAE grade in another form of grade measurement, such as the International Standards Organization (ISO). Use the chart below to help find the equivalent grade.
| Viscosity iso grade |
sae crankcase grade equivalents |
sae gear oil equivalents |
| 32 |
10W |
- |
| 46 |
20 |
- |
| 68 |
20 |
- |
| 100 |
30 |
- |
| 150 |
40 |
90 |
| 220 |
50 |
90 |
| 320 |
- |
90 |
| 460 |
- |
140 |
| 680 |
- |
140 |
For further reference, view the Fundamentals of Viscosity & Glossary of Energy Terms.