ASTM D341 Walther Viscosity–Temperature Calculator
For lubricant formulators who have a viscosity at 40 °C and 100 °C on a datasheet but need the same oil at 60 °C — this fits the ASTM D341 Walther line to those two points and reads off the third.
The tool uses log10(log10(v + 0.7)) = A - B * log10(T) correlating kinematic viscosity with temperature — the double-log transform that turns the viscosity–temperature curve into a straight line.
Viscosity-Temperature Prediction
How to Use This Calculator
- Set the °C/°F toggle to match the units of your measured temperatures.
- Enter the kinematic viscosity in cSt and the temperature of your first measured point in the Viscosity T1 and Temperature T1 fields.
- Enter the second measured point in Viscosity T2 and Temperature T2 — the two temperatures must be different.
- Type the temperature you want to evaluate into Target temperature T3.
- Read the kinematic viscosity at T3 in cSt, with the solved A and B constants shown directly below it.
FAQ
Q: What is the Walther equation used in ASTM D341?
A: It is the transform log10(log10(v + 0.7)) = A − B·log10(T), which makes kinematic viscosity v fall on a straight line against absolute temperature T; this tool solves A and B from your two measured points and applies them at T3.
Q: Do I have to enter temperatures in kelvin?
A: No — enter them in °C or °F with the toggle, and the tool converts to absolute temperature internally, because the Walther equation requires absolute temperature.
Q: What if both my measured points are at the same temperature?
A: The slope B cannot be solved from a single temperature, so the tool asks for two different temperatures before it will output a value at T3.
Q: Can I trust the result for a specification or a lab report?
A: No — this is a preliminary estimation only and is not a substitute for review by a qualified/licensed engineer; the output is an interpolation or extrapolation from your two inputs, not a measured ASTM D341 result.