Viscosity-Temperature Interpolation Calculator

Use at your own risk. Verify inputs, assumptions and results independently before applying them.

Interpolate lubricant kinematic viscosity at another temperature using the ASTM D341 Ubbelohde-Walther relationship.

Formula notes and assumptions

The simplified v + 0.7 double-log relation requires reference viscosities above 0.3 cSt for real logarithms. This mathematical bound is not a guarantee of physical validity at low viscosity. Temperatures use T = t + 273.15 in kelvin. Extreme extrapolation may be rejected when the estimate cannot be represented.

The calculation uses the ASTM D341 Ubbelohde-Walther relationship with v + 0.7.
Reference and target temperatures are entered in degrees Celsius and converted to Kelvin by adding 273.15 for this ASTM D341 calculation.
Viscosity values should be positive kinematic viscosities in cSt or mm²/s.
Use interpolation between nearby measured points for screening; extrapolation farther outside the reference range should be treated cautiously.

Input definitions

Reference temperature T1: First known temperature where lubricant kinematic viscosity is known. Unit: deg C.
Viscosity at T1: Known kinematic viscosity at the first reference temperature. Unit: cSt or mm2/s.
Reference temperature T2: Second known temperature where lubricant kinematic viscosity is known. Unit: deg C.
Viscosity at T2: Known kinematic viscosity at the second reference temperature. Unit: cSt or mm2/s.
Target temperature T3: Temperature at which the interpolated viscosity should be estimated. Unit: deg C.

Worked example

For a lubricant with kinematic viscosity 68 cSt at 40 °C and 8.6 cSt at 100 °C, enter a target temperature of 60 °C. The calculator returns approximately 28.49 cSt. At 80 °C it returns approximately 14.59 cSt. Reset restores the 60 °C example.

This estimates viscosity between the two measured temperatures for the same lubricant. Use the estimate as an operating-temperature input for a lubrication calculation, and verify it against measured data when accuracy matters. Extrapolation, phase changes and non-Newtonian behavior can invalidate the relationship.