Kinematic Viscosity Converter

Understanding Kinematic Viscosity

Kinematic viscosity describes how fast a fluid flows under the influence of gravity alone. Unlike dynamic viscosity which measures resistance to flow, kinematic viscosity accounts for fluid density, making it ideal for comparing flow behavior of different fluids.

The SI unit for kinematic viscosity is square meters per second (m²/s). Engineers commonly use centistokes (cSt) because it provides convenient numbers for lubricating oils and hydraulic fluids. One centistokes equals one millimeter squared per second (mm²/s).

Kinematic Viscosity Formula

Calculate kinematic viscosity from dynamic viscosity and density:

This relationship shows that kinematic viscosity increases when dynamic viscosity increases or when density decreases. Two fluids with the same dynamic viscosity but different densities will have different kinematic viscosities and flow at different rates under gravity.

Reynolds Number Calculation

Kinematic viscosity simplifies Reynolds number calculations for pipe flow:

Example: Water at 20°C flows through a 0.1 m diameter pipe at 2 m/s. Water kinematic viscosity equals 1.004 × 10⁻⁶ m²/s (1.004 cSt).

This Reynolds number indicates fully turbulent flow, which affects pressure drop calculations and pump selection.

Kinematic Viscosity of Common Fluids at 20°C

ISO Viscosity Grades for Industrial Lubricants

The International Organization for Standardization (ISO) established viscosity grades for industrial lubricants based on kinematic viscosity at 40°C:

Unit Conversions

Convert between kinematic viscosity units using these factors:

• 1 m²/s = 1,000,000 cSt (centistokes)
• 1 m²/s = 10,000 St (stokes)
• 1 cSt = 1 mm²/s
• 1 St = 1 cm²/s
• 1 m²/s = 10.7639 ft²/s
• 1 ft²/s = 0.092903 m²/s
• 1 cSt = 0.000001 m²/s

The stokes unit honors Sir George Stokes, who made fundamental contributions to fluid dynamics. One stokes equals 1 cm²/s, and one centistokes equals 1 mm²/s.

Applications of Kinematic Viscosity

• Lubricating oil selection and condition monitoring
• Hydraulic fluid specification for machinery
• Fuel quality testing and specification
• Pipeline flow calculations for oil and gas
• Spray nozzle design for agricultural and industrial applications
• Ink formulation for printing processes
• Blood flow studies in biomedical engineering
• Quality control in food and beverage production

Frequently Asked Questions