Poise Stokes Converter

Poise and Stokes describe two related but distinct forms of viscosity in the centimeter-gram-second system. Dynamic viscosity measures a fluid's resistance to shear: it connects shear stress with the velocity gradient produced in the fluid. Its CGS unit is the Poise, abbreviated P. Kinematic viscosity divides dynamic viscosity by density, describing momentum diffusion relative to the fluid's mass per unit volume. Its CGS unit is the Stokes, abbreviated St. The units are conveniently compatible when density is entered in grams per cubic centimeter. One Poise is one gram per centimeter-second, and one Stokes is one square centimeter per second. Kinematic viscosity in Stokes therefore equals dynamic viscosity in Poise divided by density in grams per cubic centimeter. Reversing the relation, dynamic viscosity in Poise equals kinematic viscosity in Stokes multiplied by density. This calculator performs either direction without adding an extra unit factor. Density is essential because Poise and Stokes are not simply two names for the same property. Two fluids can have the same dynamic viscosity but different kinematic viscosities if their densities differ. Conversely, fluids with equal kinematic viscosity can resist shear differently when their densities differ. A numerical one-to-one conversion occurs only when density is exactly one gram per cubic centimeter. Water is near that density under ordinary conditions, but its viscosity still varies meaningfully with temperature. Temperature and pressure should match across all entered properties. For liquids, viscosity can fall sharply as temperature rises, while density usually changes more modestly. Gas viscosity and density respond differently and can be pressure-sensitive. Mixing a viscosity measured at one temperature with density from another produces a mathematically valid quotient but not a physically consistent fluid property. Use data from the same source and operating condition whenever possible. Poise and Stokes are relatively large units. Engineering references often use centipoise and centistokes, each equal to one hundredth of its base unit. Do not enter a centipoise value as Poise or a centistokes value as Stokes without dividing it by one hundred first. In SI units, one Poise equals 0.1 pascal-second and one Stokes equals 0.0001 square meter per second. Checking those relationships is useful when combining CGS data with SI-based calculations. This converter is useful for lubrication, coatings, fuels, polymers, process fluids, and general fluid mechanics when a specification provides one viscosity form and a calculation requires the other. It assumes a homogeneous fluid with a known density and does not model non-Newtonian behavior, changing shear rate, mixtures, or uncertainty. Preserve significant figures appropriate to the source data and verify temperature, pressure, concentration, and unit prefixes before using the result in equipment design or quality control.