Viscosity Converter
Convert viscosity between units instantly. Includes conversion tables, common equivalents, and calculation formulas.
Viscosity Converter
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Formula: kinematic = dynamic / density | converted = value x (fromFactor / toFactor)
Worked example — 200 cP = 0.2 Pa·s
Formula
kinematic = dynamic / density | converted = value x (fromFactor / toFactor)
Dynamic viscosity measures resistance to flow (Pa·s). Kinematic viscosity equals dynamic viscosity divided by density (m²/s). Unit conversion multiplies by the ratio of source to target conversion factors.
Worked Examples
Example 1: Motor Oil Conversion
Problem:Convert SAE 30 motor oil viscosity of 200 cP to Pa·s.
Solution:200 cP x 0.001 = 0.2 Pa·s
Result:200 cP = 0.2 Pa·s
Example 2: Kinematic Viscosity Conversion
Problem:Convert 100 cSt to m²/s.
Solution:100 cSt x 1e-6 = 1.0 x 10^-4 m²/s
Result:100 cSt = 1.0 x 10^-4 m²/s
Frequently Asked Questions
What is the difference between dynamic and kinematic viscosity?
Dynamic viscosity (also called absolute viscosity) measures a fluid's internal resistance to flow when an external force is applied, with SI units of Pascal-seconds (Pa·s). Kinematic viscosity is the ratio of dynamic viscosity to fluid density, with SI units of m²/s. The relationship is: kinematic viscosity = dynamic viscosity / density. Water at 20 degrees Celsius has a dynamic viscosity of about 0.001 Pa·s and kinematic viscosity of about 1.004 x 10^-6 m²/s.
What is a centipoise and why is it commonly used?
A centipoise (cP) is one hundredth of a poise, which equals 0.001 Pa·s or 1 mPa·s. It is widely used because water at 20 degrees Celsius has a dynamic viscosity of approximately 1.002 cP, making it a convenient reference point. Many industrial fluids have viscosities that are easy to express in centipoise, ranging from about 1 cP for water to thousands of cP for thick oils and syrups.
How does temperature affect viscosity?
Temperature has a significant effect on viscosity. For liquids, viscosity decreases as temperature increases because higher thermal energy allows molecules to move past each other more easily. For gases, viscosity increases with temperature because faster-moving molecules transfer more momentum between layers. Motor oil viscosity, for example, can drop by 80% or more when heated from 0 to 100 degrees Celsius.
What are centistokes and how do they relate to centipoise?
Centistokes (cSt) measure kinematic viscosity, while centipoise (cP) measure dynamic viscosity. They are related by the fluid density: cSt = cP / density (in g/cm³). For water with a density near 1 g/cm³, the numerical values are nearly equal. For oil with a density of 0.9 g/cm³, a reading of 90 cP corresponds to 100 cSt. This distinction matters in engineering calculations involving fluid flow and heat transfer.
How do you convert centistokes to centipoise?
Multiply the kinematic viscosity in centistokes by the fluid density in grams per cubic centimetre to get dynamic viscosity in centipoise. The units are chosen so the factor is exactly the specific gravity. A lubricating oil at 100 cSt with a density of 0.87 g/cm3 therefore has a dynamic viscosity of 87 cP. Reverse it by dividing cP by density, and never move between the two families without a density value.
How do the poise and stokes relate to their SI counterparts?
The poise is a CGS unit equal to 0.1 pascal-second, so one centipoise is exactly one millipascal-second, roughly the viscosity of water near room temperature. On the kinematic side, one stokes is 1e-4 square metres per second, so one centistokes equals exactly one square millimetre per second. These clean equivalences are why cP and cSt survived long after the rest of CGS was retired.
What is a non-Newtonian fluid and why does it break a single viscosity value?
A Newtonian fluid has a constant ratio of shear stress to shear rate, so one number describes it at a given temperature. Non-Newtonian fluids such as polymer solutions, paints, slurries and blood change apparent viscosity with shear rate, thinning or thickening as they are pumped or stirred. For these, a converted figure is valid only at the shear rate and geometry it was measured under, so test conditions must be quoted with the number.
Which viscosity do I use in a Reynolds number calculation?
Either, provided the form matches. Reynolds number is density times velocity times characteristic length divided by dynamic viscosity, or equivalently velocity times length divided by kinematic viscosity. The kinematic form is usually less error-prone because density has already been folded in. Convert your measured value into the matching family first and keep everything in SI so the result comes out correctly dimensionless.
What does the viscosity index tell you about an oil?
The viscosity index is a dimensionless scale describing how much a fluid thins as it warms, derived from measurements at two reference temperatures. A high index means viscosity changes comparatively little across the operating range, which matters for a lubricant that must flow at cold start yet still hold a film at working temperature. It is a rate-of-change descriptor, so it cannot be converted into cP or cSt on its own.
Why must a converted viscosity always carry its measurement temperature?
Viscosity depends strongly on temperature, falling steeply as liquids warm and rising as gases warm, and for liquids the dependence is roughly exponential. Converting between units preserves whatever temperature the original measurement was taken at but cannot correct for a different one. A figure quoted as 100 cSt is meaningless until you know whether it was measured at 40 or 100 degrees Celsius.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator · Editorial policy
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