Viscosity Conversion Calculator

The Ultimate Guide to Viscosity Conversions

Viscosity is a measure of a fluid's resistance to flow. It's a property that describes a fluid's internal friction, or its "thickness." A fluid with high viscosity, like honey, flows slowly, while a fluid with low viscosity, like water, flows easily. Understanding viscosity is critical in countless fields, from automotive engineering and food science to geology and medicine. Because of its diverse applications, several different units are used to measure it. Our Viscosity Conversion Calculator is designed to provide instant and accurate conversions between the most common units for both dynamic and kinematic viscosity.

How to Use the Viscosity Converter

Our tool is divided into two independent sections: Dynamic Viscosity and Kinematic Viscosity. Conversions happen in real-time within each section.

1. Choose a Category: Decide if you are converting a dynamic or kinematic viscosity unit.
2. Select an Input Unit: Choose the field corresponding to the unit you are starting with (e.g., if you know a motor oil's viscosity in centipoise, use the "cP" box).
3. Enter Your Value: Type the number into the selected field.
4. View Instant Conversions: As you type, all other fields *within that same category* will immediately update to show the equivalent viscosity.

Dynamic vs. Kinematic Viscosity: A Critical Distinction

While often discussed together, these are two different, though related, ways of measuring a fluid's flow properties.

• Dynamic Viscosity (μ), also known as absolute viscosity, measures the fluid’s internal resistance to flow when a force is applied. It represents the shear stress required to move one layer of fluid past another. Think of it as a measure of a fluid's inherent "stickiness."
• Kinematic Viscosity (ν) is the ratio of a fluid's dynamic viscosity to its density (ρ). The formula is: ν = μ / ρ. Kinematic viscosity describes how easily a fluid flows under the influence of gravity. Two fluids could have the same dynamic viscosity (thickness), but if one is much denser, it will flow more slowly under gravity, giving it a lower kinematic viscosity.

Understanding the Units of Dynamic Viscosity

• Pascal-second (Pa·s): This is the official SI unit of dynamic viscosity. It's derived from the base units of Pascals (for pressure) and seconds (for time). It is the standard for scientific and engineering work.
• Poise (P): The Poise is the corresponding unit in the CGS (centimeter-gram-second) system. One Poise is equal to 0.1 Pa·s. It was named after the French physician Jean Léonard Marie Poiseuille.
• Centipoise (cP): A centipoise is one-hundredth of a Poise (1 P = 100 cP). This unit is extremely common because the viscosity of water at room temperature (20°C) is almost exactly 1 cP, making it a very convenient reference point.

Understanding the Units of Kinematic Viscosity

• Square meter per second (m²/s): This is the official SI unit of kinematic viscosity. It is derived directly from the SI base units for length (meter) and time (second).
• Stokes (St): The Stokes is the CGS equivalent, named after the Irish physicist Sir George Gabriel Stokes. One Stokes is equal to one square centimeter per second (cm²/s). 1 m²/s = 10,000 Stokes.
• Centistokes (cSt): A centistokes is one-hundredth of a Stokes. This is the most widely used unit for kinematic viscosity in many industries, particularly for things like fuels and lubricating oils. 1 Stokes = 100 cSt. The viscosity of water at 20°C is approximately 1 cSt.

Practical Applications for Viscosity

• Automotive Industry: The viscosity of motor oil is its most important property. The "W" in "10W-30" oil stands for winter, and the numbers relate to the oil's viscosity at different temperatures, ensuring it flows correctly to protect the engine.
• Food Science: The viscosity of products like ketchup, honey, and yogurt determines their texture, mouthfeel, and how they behave when poured or processed.
• Geology: The viscosity of magma determines the nature of a volcanic eruption. Low-viscosity magma (like in Hawaii) flows easily, creating gentle lava flows, while high-viscosity magma traps gases, leading to explosive eruptions.
• Medicine: The viscosity of blood is a critical diagnostic parameter. Abnormally high viscosity can lead to poor circulation and other health issues.

Frequently Asked Questions (FAQ)

What is the difference between dynamic and kinematic viscosity?

Dynamic viscosity (μ) measures a fluid's internal resistance to flow under shear stress (its 'thickness'). Kinematic viscosity (ν) is the ratio of dynamic viscosity to the fluid's density (ν = μ/ρ). Kinematic viscosity describes how easily a fluid flows under the force of gravity.

What is a Poise (P)?

The poise is the CGS (centimeter-gram-second) unit of dynamic viscosity, named after Jean Léonard Marie Poiseuille. One poise is equal to 0.1 Pascal-seconds (Pa·s). Centipoise (cP), which is 1/100th of a poise, is a very common unit because the viscosity of water at 20°C is almost exactly 1 cP.

What is a Stokes (St)?

The stokes is the CGS unit of kinematic viscosity, named after Sir George Gabriel Stokes. One stokes is equal to one square centimeter per second. Because it is a relatively large unit, the centistokes (cSt), which is 1/100th of a stokes, is more commonly used in industry.