Viscosity Index (VI) Calculator

Viscosity index (VI) calculator from Kinematic Viscosity (KV) at 40 °C and 100 °C according to ASTM D2270-10 and ISO 2909.

1- Viscosity Index (VI) Calculator
KV40 °C cSt (mm²/s)
KV100 °C cSt (mm²/s)
Viscosity index


2- Viscosity Calculator (KV @ 100ºC) from kinematic Viscosity at 40ºC and viscosity index (VI)
Viscosity index
KV40 °C cSt (mm²/s)
KV100 °C cSt (mm²/s)


3- Viscosity Calculator (KV @ 40ºC) from kinematic Viscosity at 100ºC and viscosity index (VI)
Viscosity index
KV100 °C cSt (mm²/s)
KV40 °C cSt (mm²/s)


Standard practice for viscosity index (VI) calculation as per ASTM D2270 and ISO 2909.

To calculate viscosity index we need viscosity of an oil both at 40°C and 100°C.

In the first row table 1, Enter kinematic viscosity (KV) at 40°C, In the same way enter kinematic viscosity @100°C in the second row. Click Calculate button to get viscosity index (VI).

Finally, press Clear button to start again.

Another possibility is to calculate kinematic viscosity from viscosity index.

Calculate Viscosity @100°C

Similarly with known viscosity index (VI) and viscosity @40°C; It is possible to calculate viscosity @100°C. For example enter viscosity index (VI) in the first row of second table. Enter kinematic viscosity (KV) @40°C in the second row. Click Calculate to get KV @100°C.

As previously stated, use Clear button to start a new calculation.

Calculate Viscosity @40°C

Likewise use calculator 3 to calculate viscosity (KV) @40°C.  Enter known viscosity index (VI) and kinematic viscosity (KV) @100°C in  table 3. Press Calculate button to calculate kinematic viscosity (KV) @40°C. As before, use Clear button to reset and calculate a new viscosity.


Lubricants Viscosity and Viscosity index

Q: What is Viscosity?

A: Viscosity is a fluid’s resistance to flow at given temperature. Therefore oil/fluids are usually measured at the same temperature to calculate viscosity. Low viscosity fluids (low resistance to move) flow or pour more easily and faster. Hence high viscosity fluids flow less easily or slower. If viscosity of fluid is high, most likely it is difficult to pour. High viscosity fluid has more resistance to flow than a low viscosity fluid. For example the viscosity of honey is higher than the water.

Q: What is viscosity index?

A: Viscosity index of a fluid is a calculated number according to ASTM D2270 or ISO 2909. Viscosity index indicates the change in fluid viscosity in dependence of temperature. It is an arbitrary, unit-less measure. Therefore higher viscosity index or higher VI means fluid is more stable and less changes in viscosity over a wide temperature ranges.

Q: How to calculate viscosity index?

A: The viscosity index of a fluid (usually oil) is calculated from its viscosity at 40 and 100°C. Common methods for viscosity index calculations are ASTM D2270 and ISO 2909. Just as an example, to calculate viscosity index we can use online viscosity index calculator or excel tools. One such viscosity index calculator is available at: