Kinematic Viscosity Converter
Convert m²/s, Stokes (St), Centistokes (cSt), ft²/s, in²/s for kinematic viscosity.
Result
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Base Unit
Relative Value
*Diagram shows values relative to the selected base unit (Square meter/second).
Unit Information
What is Square Meter per Second (m²/s)?
Square meter per second (m²/s) is the SI derived unit of kinematic viscosity. It quantifies how easily a fluid flows when influenced by gravity. A fluid with a lower m²/s value will flow more readily than a fluid with a higher value, assuming equal conditions. This unit is standard in scientific and high-level engineering contexts.
What is Square Centimeter per Second (cm²/s) or Stokes (St)?
The Stokes (symbol: St) is the CGS (centimeter-gram-second) unit of kinematic viscosity, named after Sir George Gabriel Stokes. One Stokes is equal to one square centimeter per second (1 cm²/s = 10⁻⁴ m²/s). It represents a fluid's resistance to flow under gravity in the CGS system.
What is Square Millimeter per Second (mm²/s) or Centistokes (cSt)?
Centistokes (symbol: cSt) is a commonly used CGS unit for kinematic viscosity, equal to one-hundredth of a Stokes. One centistoke is also exactly equal to one square millimeter per second (mm²/s). Water at 20°C has a kinematic viscosity of approximately 1 cSt, making it a very convenient reference. This unit is widely used in industry, especially for specifying the viscosity of oils and fuels.
What is Square Foot per Second (ft²/s)?
Square foot per second (ft²/s) is the primary imperial and US customary unit for kinematic viscosity. It is used in some engineering fields, particularly in the United States, for calculations involving fluid flow in pipelines and channels.
What is Square Inch per Second (in²/s)?
Square inch per second (in²/s) is a smaller imperial unit, used for more viscous fluids or in contexts where dimensions are measured in inches. Since 1 ft² = 144 in², it is 1/144th of a ft²/s.
Formulas
ν = μ / ρ
Kinematic viscosity (ν) is defined as the dynamic viscosity (μ) divided by the fluid's density (ρ).
1 St (Stokes) = 1 cm²/s = 10⁻⁴ m²/s
One Stokes is equal to one square centimeter per second.
1 cSt (Centistokes) = 1 mm²/s = 10⁻⁶ m²/s
One Centistoke is equal to one square millimeter per second.
1 m²/s = 10,000 Stokes
Conversion from the SI unit to the CGS unit.
1 ft²/s ≈ 929.03 cSt
Conversion between a common imperial unit and centistokes.
Key Reference Points
- Water: ~1.0 Centistokes (cSt).
- Air: ~15 cSt.
- Olive Oil: ~80-100 cSt.
- Honey: ~7000-8000 cSt.
- Mercury: ~0.11 cSt.
- Gasoline: ~0.6 cSt.
- Diesel Fuel: ~3-4 cSt.
- SAE 30 Motor Oil (at 100°C): ~11 cSt.
- Hydraulic Fluid (ISO VG 46): ~46 cSt (at 40°C).
- Glycerine: ~650 cSt.
Did You Know?
The Society of Automotive Engineers (SAE) has a system for grading motor oils (e.g., SAE 10W-30) based on their kinematic viscosity at different temperatures. The 'W' stands for 'winter' and indicates performance at low temperatures. The second number indicates viscosity at higher operating temperatures (typically 100°C). These grades correspond to specific ranges in Centistokes (cSt).
Surprisingly, at room temperature, air has a higher kinematic viscosity than water (approx. 15 cSt for air vs. 1 cSt for water). Although water is much denser and feels 'thicker' (higher dynamic viscosity), its high density reduces its kinematic viscosity (since ν = μ/ρ).
A simple way to measure kinematic viscosity for fluids like paint or varnish is with a viscosity cup (e.g., a Zahn cup). The time it takes for a known volume of liquid to flow out of an orifice at the bottom is measured, which can be correlated to a kinematic viscosity value.
The settling rate of particles in a fluid (sedimentation) is influenced by the fluid's kinematic viscosity. A higher viscosity will cause particles to settle more slowly, a principle used in various industrial and geological processes.
The speed at which a bubble rises through a liquid is inversely related to the liquid's kinematic viscosity. Bubbles rise much slower in honey (high kinematic viscosity) than in water (low kinematic viscosity).
The Engler degree (°E) is an older unit of kinematic viscosity, primarily used in Europe for petroleum products. It's based on comparing the flow time of a fluid to the flow time of water in a specific device called an Engler viscometer.
The Viscosity Index (VI) is a dimensionless number that characterizes how much an oil's kinematic viscosity changes with temperature. A higher VI indicates that the oil's viscosity changes less with temperature, which is desirable for lubricants operating over a wide temperature range.
Kinematic viscosity is a critical specification for jet fuel. It must be low enough for the fuel to be easily pumped at high altitudes and cold temperatures, but high enough to provide some lubrication for fuel system components.
SUS is another older, empirical measure of kinematic viscosity, primarily used in the US oil industry. It's the time in seconds for a specific volume of fluid to flow through a standardized orifice at a controlled temperature.
When a fluid flows over a surface, a thin 'boundary layer' forms where the fluid's velocity is slowed by viscous forces. The thickness of this layer is directly related to the fluid's kinematic viscosity.
The kinematic viscosity of honey changes dramatically with temperature. At 20°C (68°F), it's around 8000 cSt, but at 40°C (104°F), it drops to about 800 cSt, making it ten times easier to pour.
These instruments, like the Ostwald viscometer, measure kinematic viscosity by timing how long it takes for a fixed volume of fluid to flow through a narrow capillary tube under the force of gravity. The time is proportional to the kinematic viscosity.