HomeCalculatorsViscosity Index (ASTM D2270)

Viscosity Index (ASTM D2270)

Single-number rating of how much viscosity changes with temperature; high VI oils (≥ 100) stay fluid at low temperature and film-protective at high temperature.

FuelViscosityLube

Viscosity at 40 °CcStViscosity at 100 °CcStFor VI < 100 the D2270 table is linear; this page implements the linear form.

Viscosity Index

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Formula, assumptions, and limits

L, H are reference oils at the same 100 °C viscosity (low and high VI). U is the test sample viscosity at 40 °C. Modern marine cylinder oils have VI 90–110; turbine oils 95–105; hydraulic fluids 140+.

Symbol legend

Meaning	Unit	Source
Low-VI reference 40 °C viscosity	cSt	ASTM D2270 table
High-VI reference 40 °C viscosity	cSt	ASTM D2270 table
Sample viscosity at 40 °C	cSt	input
Viscosity index	-	result