Viscosité cinématique

About Kinematic Viscosity Conversion

Kinematic viscosity is dynamic viscosity divided by fluid density—it describes how fast a fluid flows under the influence of gravity alone, without any applied force. This fundamental property determines how quickly a fluid drains, how long it takes to flow through a calibrated tube, and how it behaves in gravity-driven flow situations. The kinematic viscosity directly measures what matters for gravity-fed lubrication systems and drainage applications.

The SI unit is square meters per second (m²/s), but centistokes (cSt) is the overwhelming practical standard, especially for lubricants and petroleum products. Motor oil grades (SAE 5W-30, etc.) are defined by kinematic viscosity at standard temperatures—100°C for the hot rating, -35°C for the cold (W) rating. The centistokes unit persists because it produces convenient numbers: water is about 1 cSt at 20°C, light oils are 10-50 cSt, and heavy lubricants are 100-500 cSt.

Our converter handles all standard kinematic viscosity units for lubrication engineering, petroleum refining, and fluid system design.

Common Kinematic Viscosity Conversions

Kinematic Viscosity Unit Reference

Square meter per second (m²/s) – The SI unit for kinematic viscosity. Impractically large for most fluids—water is about 10⁻⁶ m²/s, requiring scientific notation. Reserved for theoretical calculations and dimensional analysis. 1 m²/s = 10,000 Stokes = 1,000,000 cSt. Rarely used in practical specifications.

Centistokes (cSt) – The dominant practical standard for lubricants, petroleum products, and industrial fluids worldwide. 1 cSt = 1 mm²/s = 10⁻⁶ m²/s. SAE oil grades are defined by kinematic viscosity in cSt: SAE 30 is 9.3-12.5 cSt at 100°C, SAE 40 is 12.5-16.3 cSt. ASTM and ISO lubricant standards use cSt exclusively. Water ≈ 1 cSt at 20°C provides an intuitive reference point.

Stokes (St) – CGS unit equal to 1 cm²/s = 100 cSt. Named after George Stokes. Less common in modern practice but still appears in older scientific literature, some European references, and conversion tables. 1 St = 0.0001 m²/s.

Square millimeter per second (mm²/s) – Numerically identical to centistokes (1 mm²/s = 1 cSt exactly). Increasingly preferred in ISO standards and scientific publications that avoid non-SI units. Provides SI compatibility while maintaining the convenient scale of cSt.

Square foot per second (ft²/s) – US customary unit occasionally found in older American engineering references. 1 ft²/s = 929 St = 92,903 cSt. Rarely used in modern practice; most US lubricant specifications use cSt.

Learn More

Explore our in-depth guides on this topic:

• Oil Viscosity Grades Explained