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Calcimator

Lubricant Viscosity Calculator

Calculate operating viscosity from temperature using the Walther equation and classify by ISO VG grade.

Inputs

cSt
cSt
°F

Results

Viscosity at Operating Temp

20.28 cSt

ISO VG Grade46
VI Quality Rating3
Relative Film Thickness Index4.5
Viscosity Ratio (40°C/100°C)7.7
How to Use This Calculator
  1. Enter Kinematic Viscosity at 40°C, Kinematic Viscosity at 100°C, and Operating Temperature.
  2. Set Viscosity Index (VI).
  3. Review the Viscosity at Operating Temp (cSt) result.
  4. Use ISO VG Grade and VI Quality Rating to inform your decision.
  5. Use the chart to visualize the results and explore different scenarios by adjusting inputs.

How the result changes with Operating Temperature

Operating TemperatureViscosity at Operating Temp
2841.9 cSt
5732.32 cSt
1235.44 cSt
1782.42 cSt

What each input means

Kinematic Viscosity at 40°C
Kinematic viscosity measured at 40°C (104°F) in centistokes. Found on the product data sheet.
Kinematic Viscosity at 100°C
Kinematic viscosity measured at 100°C (212°F) in centistokes.
Operating Temperature
Actual operating temperature of the equipment in °C.
Viscosity Index (VI)
Viscosity index per ASTM D2270. Mineral oils: 80–100, Group II: 100–120, Synthetic: 130+.

What each result means

VI Quality Rating
1=Low, 2=Medium, 3=High, 4=Very High (synthetic)

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Kinematic Viscosity at 40°C = 68, Kinematic Viscosity at 100°C = 8.8, Operating Temperature = 70, Viscosity Index (VI) = 100 = 4 input(s) provided
  2. Calculate Viscosity at Operating Temp
    Viscosity at Operating Temp = Math
    20.28 = 20.28
  3. Calculate ISO VG Grade
    ISO VG Grade
    46 = 46
  4. Calculate VI Quality Rating
    VI Quality Rating
    3 = 3

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