ASTM D2270 Standard

Viscosity Index Calculator

Calculate the Viscosity Index (VI) of a lubricant instantly with our ASTM D2270-based calculator. Enter kinematic viscosities at 40 °C and 100 °C to see how stable your oil’s viscosity is across temperature changes. This tool follows the official ASTM D2270 methodology and is suitable for engine oils, hydraulic fluids, gear oils, and other lubricants where VI matters.

Viscosity Index (VI) Calculator

Compute VI from kinematic viscosities at 40 °C and 100 °C (ASTM D2270).

Viscosity Index (VI)

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Methodology

This tool follows ASTM D2270. Measure kinematic viscosity at 40 °C and 100 °C per ASTM D445, then compute VI.

Notation: U = KV40 (cSt), Y = KV100 (cSt). Using Y, the standard provides reference values L and H (both at 40 °C) for VI = 0 and VI = 100 oils.

For VI ≤ 100: VI = ((L − U) / (L − H)) × 100

For VI > 100: VI = ((10N − 1) / 0.00715) + 100, where N = (log H − log U) / log Y.

Note: This calculator uses smooth approximations of the D2270 L/H tables within common engine‑oil ranges. For certification, use the official tables.

Learn how VI is calculated (ASTM D2270 →)

How the Viscosity Index Calculator Works

This calculator uses your measured kinematic viscosities at 40 °C and 100 °C, following ASTM D445, to determine VI according to ASTM D2270.

  • KV40: Kinematic viscosity at 40 °C (in centistokes, cSt)
  • KV100: Kinematic viscosity at 100 °C (in centistokes, cSt)
  • Reference Values: The calculator finds L and H (reference viscosities for VI = 0 and VI = 100) from standard tables.
  • Formula Selection: If your oil’s VI is 100 or less, the calculator uses the standard VI ≤ 100 formula. For oils above 100, it applies the logarithmic VI > 100 formula.

Why Viscosity Index Matters

The Viscosity Index measures how much an oil’s viscosity changes with temperature. A higher VI means the oil stays closer to its intended thickness across operating conditions, improving cold-start protection and high-temperature film strength.

Oils with VI above 150 are common in high-performance synthetic engine oils, while industrial and mineral-based oils may have VI values closer to 100

FAQ

Frequently Asked Questions

What inputs do I need for the Viscosity Index Calculator?

You need two values: the lubricant’s kinematic viscosity at 40 °C (KV40) and at 100 °C (KV100), measured in centistokes (cSt) according to ASTM D445.

Does this calculator follow the ASTM D2270 standard?

Yes. The calculator uses the official ASTM D2270 methodology, including separate formulas for VI ≤ 100 and VI > 100, and reference values for L and H.

Is the Viscosity Index Calculator free to use?

Yes. The tool is completely free to use on LubeGuide.org and can be accessed on any device with a web browser.

What does a higher Viscosity Index mean?

A higher Viscosity Index means the lubricant’s viscosity changes less with temperature, indicating better stability and performance across cold and hot conditions.

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