Viscosity Index Calculator Widman

Viscosity Index Formula:

\[ VI = \frac{(L - U)}{(L - H)} \times 100 \]

Viscosity of reference oil at 40°C (L):

cSt

Viscosity of test oil at 40°C (U):

cSt

Viscosity of reference oil at 100°C (H):

cSt

Viscosity Index (VI):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Viscosity Index?

Definition: The Viscosity Index (VI) is a dimensionless number that indicates how much a fluid's viscosity changes with temperature.

Purpose: It helps engineers and lubricant specialists evaluate the temperature-viscosity behavior of oils.

2. How Does the Calculator Work?

The calculator uses the Widman formula:

\[ VI = \frac{(L - U)}{(L - H)} \times 100 \]

Where:

\( VI \) — Viscosity Index (dimensionless)
\( L \) — Viscosity of reference oil at 40°C (cSt)
\( U \) — Viscosity of test oil at 40°C (cSt)
\( H \) — Viscosity of reference oil at 100°C (cSt)

Explanation: The formula compares how the test oil's viscosity changes relative to two reference oils with known viscosity-temperature characteristics.

3. Importance of Viscosity Index

Details: Higher VI values indicate less viscosity change with temperature. High VI oils maintain more stable viscosity across operating temperatures.

4. Using the Calculator

Tips: Enter the viscosity values in centistokes (cSt) for all three parameters. Ensure (L - H) is not zero.

5. Frequently Asked Questions (FAQ)

Q1: What is a good VI value?
A: Typical values range from 0-200. Higher is better - mineral oils: 80-120, synthetic oils: 120-200.

Q2: Why measure at 40°C and 100°C?
A: These are standard temperatures for viscosity measurement in the petroleum industry.

Q3: What if I get a negative VI?
A: Check your measurements - negative VI suggests unusual viscosity-temperature behavior.

Q4: How accurate is this calculation?
A: The Widman formula provides standard VI values comparable to ASTM D2270 method.

Q5: Can I use this for any oil?
A: Yes, but results are most meaningful for petroleum-based lubricating oils.