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Viscosity Conversion

ν = μ/ρ. Dynamic (μ) in Pa·s, P, cP. Kinematic (ν) in m²/s, St, cSt. 1 P = 0.1 Pa·s; 1 St = 10⁻⁴ m²/s.

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Water 20°C: μ ≈ 1 mPa·s, ν ≈ 1 cSt 1 P = 0.1 Pa·s; 1 cP = 1 mPa·s 1 St = 10⁻⁴ m²/s; 1 cSt = 1 mm²/s ASTM D445, ISO 3104 for measurement

Key quantities
μ/ρ
ν
Key relation
ν × ρ
μ
Key relation
0.1 Pa·s
1 P
Key relation
10⁻⁴ m²/s
1 St
Key relation

Ready to run the numbers?

Why: Viscosity units vary by industry. Reynolds number needs kinematic ν; stress calculations need dynamic μ.

How: ν = μ/ρ links them. Input two of μ, ν, ρ. Convert units with standard factors.

Water 20°C: μ ≈ 1 mPa·s, ν ≈ 1 cSt1 P = 0.1 Pa·s; 1 cP = 1 mPa·s
Sources:NIST Physical ConstantsASTM D445

Run the calculator when you are ready.

Solve the EquationConvert between viscosity units

💧 Water at 20°C

Pure water at room temperature - reference fluid

🛢️ Motor Oil (SAE 10W-30)

Typical motor oil viscosity for automotive applications

🍯 Honey

High viscosity fluid - typical honey at room temperature

🧪 Glycerin

Common laboratory fluid with moderate viscosity

🌬️ Air at 20°C

Dry air at sea level - very low viscosity

💧 Water Kinematic Viscosity

Convert kinematic viscosity of water to dynamic

Input Parameters

For educational and informational purposes only. Verify with a qualified professional.

🔬 Physics Facts

💧

ν = μ/ρ — kinematic from dynamic and density

— NIST

📐

1 P = 0.1 Pa·s; 1 cP = 1 mPa·s

— ASTM D445

⚡

1 St = 10⁻⁴ m²/s; 1 cSt = 1 mm²/s

— ISO 3104

📏

Water 20°C: μ ≈ 1 mPa·s

— Engineering Toolbox

What is Viscosity?

Viscosity is a measure of a fluid's resistance to flow and deformation. It quantifies the internal friction within a fluid when it flows. There are two main types of viscosity: dynamic viscosity (μ) and kinematic viscosity (ν). Understanding viscosity is crucial in fluid mechanics, chemical engineering, and many industrial applications.

Key Concepts

  • Dynamic Viscosity (μ): Also called absolute viscosity, measures the resistance to flow when an external force is applied. Units include Pa·s, Poise (P), and centipoise (cP).
  • Kinematic Viscosity (ν): The ratio of dynamic viscosity to density, representing the fluid's resistance to flow relative to its density. Units include m²/s, Stokes (St), and centistokes (cSt).
  • Relationship: ν = μ/ρ, where ρ is the fluid density. This fundamental relationship allows conversion between dynamic and kinematic viscosity.
  • Temperature Dependence: Viscosity typically decreases with increasing temperature for liquids and increases for gases.

Dynamic Viscosity

Measures internal friction when force is applied. Common units: Pa·s, Poise (P), centipoise (cP). Higher values indicate thicker, more viscous fluids.

Kinematic Viscosity

Dynamic viscosity divided by density. Common units: m²/s, Stokes (St), centistokes (cSt). Useful for comparing fluids with different densities.

Conversion

Convert between dynamic and kinematic viscosity using density: ν = μ/ρ. Essential for fluid flow calculations and Reynolds number determination.

How Viscosity Conversion Works

Viscosity conversion involves converting between different unit systems and between dynamic and kinematic viscosity types. The conversions use standard conversion factors and the fundamental relationship between viscosity and density.

Key Conversion Steps

1. Unit Conversion Within Same Type

Convert between units of the same viscosity type (e.g., Pa·s to Poise):

1 Pa·s = 10 P = 1000 cP
1 P = 0.1 Pa·s = 100 cP
1 cP = 0.001 Pa·s = 0.01 P

Similar conversions apply for kinematic viscosity units

2. Dynamic to Kinematic Conversion

Convert dynamic viscosity to kinematic viscosity using density:

ν = μ/ρ

Where ν is kinematic viscosity, μ is dynamic viscosity, and ρ is density

3. Kinematic to Dynamic Conversion

Convert kinematic viscosity to dynamic viscosity:

μ = ν × ρ

Rearranged form of the fundamental relationship

4. Unit System Conversions

Convert between metric and imperial units:

1 lb/(ft·s) = 1.48816 Pa·s
1 ft²/s = 0.092903 m²/s

Imperial to metric conversion factors

When to Use Viscosity Conversion

Viscosity conversion is essential in many engineering and scientific applications where different unit systems are used or when converting between dynamic and kinematic viscosity is required.

Fluid Mechanics

Calculate Reynolds numbers, flow regimes, and pressure drops. Convert between viscosity units used in different standards.

Chemical Engineering

Process design, pump sizing, and pipeline calculations. Convert viscosity data from different sources and standards.

Lubrication Engineering

Select appropriate lubricants, convert between SAE grades and SI units, and analyze viscosity-temperature relationships.

Viscosity Conversion Formulas

Comprehensive formulas for converting between viscosity units and types.

Core Formulas

Dynamic to Kinematic Viscosity

ν = μ/ρ

Fundamental relationship between viscosity types

Kinematic to Dynamic Viscosity

μ = ν × ρ

Rearranged form

Poise Conversions

1 P = 0.1 Pa·s = 100 cP
1 cP = 0.001 Pa·s = 0.01 P

CGS unit conversions

Stokes Conversions

1 St = 10⁻⁴ m²/s = 100 cSt
1 cSt = 10⁻⁶ m²/s = 0.01 St

Kinematic viscosity CGS units

Imperial Unit Conversions

1 lb/(ft·s) = 1.48816 Pa·s
1 ft²/s = 0.092903 m²/s

US customary unit conversions

❓ Frequently Asked Questions

What is the difference between dynamic and kinematic viscosity?

Dynamic viscosity (μ) measures a fluid's resistance to flow when an external force is applied. Kinematic viscosity (ν) is dynamic viscosity divided by density (ν = μ/ρ). Dynamic viscosity is used for force calculations, while kinematic viscosity is useful for comparing fluids with different densities.

Why are Poise and Stokes still used if SI units exist?

Poise (P) and Stokes (St) are CGS units that remain common in engineering, especially for petroleum products, lubricants, and chemical processing. Many industry standards (ASTM, ISO) still reference these units, making conversions essential for practical applications.

How does temperature affect viscosity?

For liquids, viscosity typically decreases with increasing temperature (water viscosity drops from 1.792 mPa·s at 0°C to 0.282 mPa·s at 100°C). For gases, viscosity increases with temperature. This temperature dependence is critical for accurate viscosity measurements and conversions.

What is a typical viscosity range for common fluids?

Air: ~0.018 mPa·s, Water: ~1 mPa·s, Motor oil: 10-200 mPa·s, Honey: ~10,000 mPa·s. Viscosity spans many orders of magnitude, so proper unit conversion is essential for accurate calculations.

How do I convert between dynamic and kinematic viscosity?

Use the relationship ν = μ/ρ, where ν is kinematic viscosity, μ is dynamic viscosity, and ρ is density. You need the fluid density to perform this conversion. The calculator handles this automatically when you provide density values.

What units are most commonly used in industry?

For dynamic viscosity: centipoise (cP) is most common, especially in petroleum and chemical industries. For kinematic viscosity: centistokes (cSt) is standard. SI units (Pa·s and m²/s) are used in scientific and engineering calculations.

Why is viscosity important in engineering applications?

Viscosity determines flow rates, pressure drops, pump sizing, heat transfer, and lubrication effectiveness. Incorrect viscosity values can lead to equipment failure, inefficient operation, or safety hazards. Accurate conversion between units is critical for proper design.

How accurate are viscosity conversions?

Unit conversions are mathematically exact. However, viscosity values themselves depend on temperature, pressure, and fluid composition. Always verify that viscosity data matches your operating conditions. The calculator provides conversions accurate to the precision of your input values.

📚 Official Data Sources

NIST Physical Constants

Official NIST values for fundamental physical constants and viscosity standards

Last Updated: 2026-02-07

ASTM D445 - Kinematic Viscosity

Standard test method for kinematic viscosity of transparent and opaque liquids

Last Updated: 2026-02-07

Engineering Toolbox - Viscosity

Comprehensive viscosity conversion tables and fluid properties database

Last Updated: 2026-02-07

ISO 3104 - Petroleum Viscosity

ISO standard for determination of kinematic viscosity of petroleum products

Last Updated: 2026-02-07

⚠️ Disclaimer

This calculator is for educational and engineering design purposes. Viscosity values depend on temperature, pressure, and fluid composition. Always verify calculations against manufacturer specifications and industry standards (ASTM, ISO). For critical applications, consult a licensed engineer or refer to official viscosity measurement standards. Unit conversions are mathematically exact, but actual fluid properties may vary with conditions.

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