Viscosity Converter

Viscosity measures a fluid's resistance to flow and deformation. It is one of the most important properties in fluid mechanics, affecting everything from engine lubrication to food processing. There are two types of viscosity: dynamic (absolute) viscosity, which measures internal resistance to flow, and kinematic viscosity, which is dynamic viscosity divided by fluid density. This professional viscosity converter handles both types, providing instant, accurate conversions between commonly used units.

Dynamic Viscosity: Pascal-Seconds and Poise

Pascal-second (Pa·s) is the SI unit of dynamic viscosity. It represents the shear stress in Pascals required to move one layer of fluid past another at a specific rate. One Pascal-second equals one kilogram per meter-second. Water at 20°C has a dynamic viscosity of about 0.001 Pa·s (1 mPa·s), while honey measures around 2-10 Pa·s depending on temperature and moisture content. The CGS unit, Poise (P), is still widely used: 1 Pa·s = 10 Poise.

Centipoise: The Practical Standard

Centipoise (cP) is the most commonly used unit for dynamic viscosity in industry because it provides convenient numbers for typical fluids. One centipoise equals one millipascal-second (mPa·s). Water at 20°C has a viscosity of approximately 1 cP, making it a natural reference point. Motor oils are typically rated SAE 5W-30, where the viscosity at operating temperature might be 10-12 cP. Maple syrup measures around 150-200 cP, while peanut butter exceeds 150,000 cP. The pharmaceutical, food, and petroleum industries extensively use centipoise specifications.

Kinematic Viscosity: Stokes and Centistokes

Kinematic viscosity equals dynamic viscosity divided by density, representing how easily a fluid flows under gravity. The SI unit is square meters per second (m²/s), but Stokes (St) and centistokes (cSt) are more common in practice. One Stokes equals 10⁻⁴ m²/s, and one centistokes equals 10⁻⁶ m²/s. Kinematic viscosity is what viscometers typically measure directly (by timing how long fluid takes to flow through a capillary). Engine oils are often rated by their kinematic viscosity at 40°C and 100°C.

Temperature Effects on Viscosity

Viscosity is highly temperature-dependent, which is why specifications always include temperature. For most liquids, viscosity decreases as temperature increases. Water's viscosity drops from 1.79 cP at 0°C to 0.28 cP at 100°C. Motor oil viscosity might change from 300 cP at -20°C to just 5 cP at 100°C. This is why multi-grade oils (e.g., 10W-40) are formulated with additives to maintain useful viscosity across a wide temperature range.

Key Conversion Factors

• 1 Pa·s = 1,000 cP = 10 Poise = 1,000 mPa·s
• 1 cP = 0.001 Pa·s = 0.01 Poise = 1 mPa·s
• 1 St = 100 cSt = 10⁻⁴ m²/s = 1 cm²/s
• 1 cSt = 0.01 St = 10⁻⁶ m²/s = 1 mm²/s

Practical Applications

• Automotive: Engine oil selection, transmission fluid, and hydraulic systems
• Food Processing: Sauce consistency, chocolate tempering, and beverage quality
• Pharmaceuticals: Drug formulation, injection solutions, and topical preparations
• Coatings & Paints: Application properties, leveling, and drying characteristics
• Petroleum: Crude oil classification, pipeline transport, and refinery operations
• Chemical Engineering: Pump selection, mixing operations, and heat transfer