## Standard Practice for Viscosity-Temperature Charts for Liquid Petroleum Products

If you know the viscosity of a particular type of oil at two temperatures (like 40 and 100°C) , it is possible to calculate it at a different temperature (ASTM D341). In addition to this, one can calculate the oil viscosity at the operating temperature of the equipment. See examples given at the end of this page.

### Calculator for kinematic viscosity extrapolation

Viscosity 1 (mm2/s) cSt
At Temperature (°C)
Viscosity 2 (mm2/s) cSt
At Temperature (°C)
Calculate Viscousity at (°C)
Result

### Example 1: Calculating viscosity at the operating temperature

SAE-140 gear oil has a 28 cSt kinematic viscosity at 100°C and 404 cSt at 40°C. Calculate lubricant viscosity at 60°C operating temperature.

Viscosity at 60°C=132.126 (mm2/s)

### Example 2: Calculate viscosity index

ASTM D2270 covers the procedures for calculating the viscosity index of oils from the kinematic viscosities at 40 and 100°C. For low flash point lubricants when conditions prevent testing at 100°C. An estimate of 100°C kinematic viscosity can be calculated by testing the lubricant at low temperatures.

Measured viscosity (ASTM D445) at 40°C= 68 cSt
Measured viscosity (ASTM D445) at 80°C= 14.85 cSt
Calculated viscosity at 100°C=8.8 cSt (use above calculator)
Use Viscosity index calculator to calculate viscosity index from kinematic viscosities at 40 (68 cSt) and 100°C (8.8 cSt).

Viscosity index=102