Viscosity Index & Temperature Calculator
Compute VI and the viscosity–temperature curve from ν₄₀ and ν₁₀₀
Enter the kinematic viscosity at 40 °C and 100 °C and the tool returns the ASTM D2270 viscosity index along with the ASTM D341 (Walther) viscosity at any temperature.
1Enter kinematic viscosities
Viscosity at 40 °C
Viscosity at 100 °C
2Results
Viscosity Index (ASTM D2270)154VI > 100 (higher-VI regime)
Reference L0-VI reference at Y141.96mm²/s
Reference H100-VI reference at Y89.61mm²/s
SAE J300 high-temp gradeSAE 30
Low-temperature (W) grades require CCS / MRV data and are not computed here.Viscosity–Temperature Curve (ASTM D341 / Walther)
Predicted viscosity17.41mm²/s
The curve fits the Walther equation through the two input points (40 °C / 100 °C). White markers show the inputs; the cyan marker and vertical line track the slider temperature.
A7.82297
B3.03118
Y = ν₁₀₀10.900 mm²/s
U = ν₄₀64.000 mm²/s
Assumptions & Limitations
- VI uses the ASTM D2270 L/H reference table with linear interpolation for Y ≤ 70 mm²/s, and the standard's polynomials (L = 0.8353·Y² + 14.67·Y − 216, H = 0.1684·Y² + 11.85·Y − 97) for Y > 70.
- The viscosity–temperature curve extrapolates a two-point Walther fit, log₁₀(log₁₀(ν + 0.7)) = A − B · log₁₀(T). Real oils may deviate noticeably below 0 °C or above 150 °C.
- We assume Newtonian behaviour with no shear-rate dependence. Multigrade oils may show temporary or permanent shear loss (TSL/PSL) in service due to polymer additives.
- SAE J300 grading shown here is for high-temperature classification only. W-grade classification requires CCS / MRV data and is out of scope.
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