SAE Viscosity Grade
Definition
The Society of Automotive Engineers (SAE J300) classification of motor oil viscosity: the 'W' number specifies low-temperature cranking viscosity; the trailing number specifies kinematic viscosity at 100°C. Multigrade oils (e.g. 5W-30) meet both specifications through base oil selection and viscosity index improver polymers.
- Standard
- SAE J300
- W number meaning
- Low-temperature cranking viscosity
- Second number meaning
- Kinematic viscosity at 100°C
- Example multigrade
- 5W-30
Common questions
How does an SAE grade help identify an unknown oil sample in casework?+
Measuring the sample's viscosity at the specified temperatures and comparing it against the SAE J300 bands can narrow the possible grade of a recovered oil, which is useful when comparing a spill, stain, or container residue to a suspected source product.
Why do multigrade oils carry two numbers instead of one?+
A single-viscosity oil only performs well across a narrow temperature range, so multigrade oils use viscosity index improver polymers so the oil behaves like the low W number when cold and the higher number when hot, giving usable protection across a wider temperature range.
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