BIZOMAT MAKEOS · Units
Oil Viscosity Unit Conversion (cSt, cP, SUS, Reyn)
What is this oil viscosity in centistokes, centipoise, Saybolt seconds and reyns?
Conversion between kinematic viscosity (centistokes, mm²/s), absolute or dynamic viscosity (centipoise, pascal-seconds, reyn) and Saybolt Universal Seconds at 40 °C and 100 °C, using the oil’s density, by the handbook relations.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Given value is | choice | Unit of the value you have. |
| Value | Viscosity value in that unit. | |
| Oil specific gravity (density in g/cm³) | Specific gravity of the oil at the measurement temperature. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Given value is
- What it is
- The unit your known viscosity is quoted in: kinematic centistokes, dynamic centipoise or reyn, or Saybolt Universal Seconds at one of two test temperatures.
- Units and format
- Choose one of 5 options from the list: Kinematic, cSt (mm²/s); Dynamic, cP (mPa·s); SUS at 100 °F (40 °C); SUS at 210 °F (100 °C); Dynamic, reyn (lbf·s/in²).
- Example
- The form opens with “Kinematic, cSt (mm²/s)” selected as a worked example. Choose the option that matches your case.
- Get it right
- cSt and SUS are kinematic; cP and reyn are dynamic and need the specific gravity to convert.
What this means: Value
- What it is
- The viscosity figure you already have from the oil data sheet, lubricant specification or oil analysis report, in the unit chosen above.
- Units and format
- Enter a plain number with no unit. The form accepts 0.000001 or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 68 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Note the temperature it was measured at: viscosity changes strongly with temperature and this conversion does not correct for it.
What this means: Oil specific gravity (density in g/cm³)
- What it is
- The density of the oil divided by the density of water, which numerically equals its density in g/cm³, at the same temperature as the viscosity.
- Units and format
- Enter a plain number with no unit. The form accepts 0.5 to 2. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.88 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Dynamic viscosity equals kinematic viscosity times specific gravity.
- Get it right
- Only conversions between kinematic and dynamic units use it; use the value at the viscosity’s temperature where the data sheet gives one.
Method and formulas
- cSt = cP ÷ specific gravity; cP = specific gravity × cSt.
- SUS ≈ 4.632 × cSt at 100 °F (40 °C) and 4.664 × cSt at 210 °F (100 °C).
- 1 reyn = 68,950 poise = 6.895 × 10⁶ cP; 1 cP = 1 mPa·s.
- Example: 68 cSt at specific gravity 0.88 is 59.84 cP and about 314.98 SUS at 40 °C.
Limitations
- The SUS multipliers apply to the higher viscosities; low viscosities need the ASTM D2161 table.
- Viscosity must be converted at the same temperature as it was measured.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Compare oil specifications quoted in different units
- Convert a viscosity for a bearing film calculation
- Check an older SUS specification against an ISO VG grade
Who it is for
- Lubrication technicians
- Reliability engineers
- Design engineers
What you get
- Kinematic viscosity
- Dynamic viscosity
- Saybolt seconds
Interpreting the result
- Absolute viscosity is what an oil-film calculation needs; kinematic is what grades and oil analysis report.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2425–2426. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
What viscosity measures
What it covers: Define viscosity from the shear stress in a moving film, tell dynamic from kinematic viscosity, convert between units, and see which one each calculation needs.
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Open the Oil Viscosity Unit Conversion (cSt, cP, SUS, Reyn) calculator