Kinematic viscosity converter — cSt, mm²/s, stokes and ft²/s

How to use the kinematic viscosity converter

1. Enter the viscosity in Value. The default is 1.
2. Pick its unit in From, such as centistokes (cSt).
3. Pick the unit you want in To, such as m²/s. The default converts 1 cSt to m²/s.
4. The table below the result lists all eight units. Use the swap button to reverse the direction.

What it does and when to use it

Kinematic viscosity measures how quickly a fluid flows under its own weight. It is the figure on lubricating oil, hydraulic oil and fuel specifications, usually in cSt or mm²/s. Fluid mechanics formulas, such as the Reynolds number for pipe flow, need it in m²/s, and older US references use ft²/s.

Use this tool to put a data-sheet cSt value into an SI formula, to read a US handbook table, or to compare two suppliers who use different units. Because it is an area per time unit, every factor is a length squared; the area converter explains why squared factors grow so fast. If you have mixed dynamic and kinematic figures, the combined viscosity converter sorts them into the right group.

How it works

Every unit is stored in square metres per second.

The stokes is the CGS unit, defined as 1 cm²/s, and NIST lists it as 10⁻⁴ m²/s. The foot and inch are exact international definitions, so every factor here is exact. Results are shown to 12 significant figures.

Worked examples

A hydraulic oil at 46 cSt. 46 cSt = 0.000046 m²/s, the same as 0.46 stokes or about 0.000495 ft²/s.

A US table value. 1 ft²/s = 92,903.04 centistokes (cSt), or 144 in²/s.

From mm²/s to stokes. 100 mm²/s = 1 stokes (St), or 100 cSt.

Limits and tips

• Check the temperature printed next to any viscosity. The converter changes units only, not conditions.
• Water is close to 1 cSt at room temperature, which makes a useful mental check.
• Results smaller than 10⁻⁹ switch to scientific notation.