Centistokes

Centistokes (cSt) is a unit of kinematic viscosity in the centimeter–gram–second (CGS) system. It is defined as one hundredth of a Stokes, with 1 Stokes equal to 1 centimeter squared per second. Since 1 centimeter equals 0.01 meters, 1 Stokes equals 1×10−4 m^2/s, and therefore 1 centistoke equals 1×10−6 m^2/s. The centistoke is used to express the kinematic viscosity ν of a fluid, which relates dynamic viscosity μ and density ρ by ν = μ/ρ.

In practice, ν is measured with viscometers or capillary methods at a specified temperature. Because density and viscosity depend on temperature, cSt values are usually reported at a standard temperature such as 20°C or 40°C, depending on industry convention. The measurement provides a ν in cSt, which can be converted to SI units via ν (m^2/s) = cSt × 1×10−6.

Applications and typical ranges: The centistoke is widely used in petroleum, lubricants, and polymer science to describe liquids in a practical viscosity range. Substances with low viscosity, such as water, are about 1 cSt at room temperature, while mineral oils commonly fall in the range of a few to tens of cSt at common operating temperatures. Heavy fuels or syrups can exceed hundreds or thousands of cSt, especially at lower temperatures, with viscosity decreasing as temperature rises.

History and naming: The unit is named after Sir George Gabriel Stokes. It remains a standard practical unit for kinematic viscosity in many engineering contexts, even as SI-based units are used for formal documentation.