Kinematic viscosity — how easily a fluid flows under gravity, independent of the force pushing it — is measured in a mix of units depending on the field and era. Lubricant and oil datasheets almost always use centistokes, engineering references often use the SI square-meter-per-second, and older texts sometimes use stokes or the US customary square-foot-per-second. This converter translates between all four and links kinematic viscosity to its close relative, dynamic viscosity, via density.

Why kinematic viscosity has so many units

The SI unit for kinematic viscosity is the square meter per second (m²/s), but it rarely appears on a datasheet because it produces awkward numbers for common fluids — water's kinematic viscosity is about 1e-6 m²/s, a value few people find intuitive. Centistokes avoids this problem: water comes out to almost exactly 1 cSt, which is why centistokes became the default unit on engine oil, hydraulic fluid, and fuel specifications. Stokes (100 times larger than centistokes) persists in older fluid-mechanics literature and some CGS-unit engineering contexts. Square feet per second occasionally appears in US customary engineering references.

How the conversion works

This calculator converts every unit through a single common base — square meters per second (m²/s), the SI unit for kinematic viscosity. Your input value is first converted to m²/s using that unit's fixed factor, then converted from m²/s into the target unit. This two-step approach means adding a new unit only requires one conversion factor, and it guarantees that converting A → B gives the same answer as converting A → m²/s → B, with no rounding surprises from unit-pair-specific shortcuts.

Kinematic vs. dynamic viscosity

Kinematic viscosity (ν) and dynamic viscosity (μ) are related by density: ν = μ / ρ, or equivalently μ = ν × ρ. Kinematic viscosity describes how a fluid flows under gravity alone — it's what you'd measure timing a fluid drain through a calibrated tube. Dynamic viscosity describes the force needed to shear the fluid, independent of how dense it is. The two are easy to confuse because both show up on fluid datasheets, but converting between them always requires knowing the fluid's density. The To Dynamic tab on this page performs that conversion directly: enter your kinematic viscosity and a density, and it returns the equivalent dynamic viscosity in pascal-seconds.