Water Viscosity Calculator

Viscosity is a measure of a fluid's resistance to flow or deformation. A fluid with high viscosity (like honey) flows slowly, while a fluid with low viscosity (like water) flows easily. It plays a key role in engineering calculations involving fluid dynamics, heat transfer, and pipe flow.

At 20°C (68°F), the dynamic viscosity of water is approximately 1.002 mPa·s (or 1.002 cP), and the kinematic viscosity is about 1.004 mm²/s (cSt). These values decrease significantly as temperature rises.

Water viscosity decreases as temperature increases. At 0°C it is about 1.793 mPa·s, dropping to around 0.282 mPa·s at 100°C and even lower at higher temperatures. This inverse relationship is important for heating, cooling, and pumping system design.

Dynamic viscosity (η) measures a fluid's internal resistance to flow under an applied force, expressed in Pa·s or mPa·s. Kinematic viscosity (ν) is dynamic viscosity divided by the fluid density (ν = η/ρ), expressed in m²/s or mm²/s. Kinematic viscosity is useful in Reynolds number calculations for flow regime analysis.

A common approach uses the Vogel-Fulcher-Tammann (VFT) equation or polynomial fits to experimental data. This calculator uses an empirical formula based on validated reference data to compute dynamic viscosity (in mPa·s) from the input temperature, then divides by water density to obtain kinematic viscosity.

This calculator is valid for liquid water between 0°C and 370°C (32°F to 700°F, or 273 K to 643 K). Near 100°C at atmospheric pressure water begins to boil, but viscosity values at higher temperatures apply under elevated pressure conditions.

Dynamic viscosity is commonly expressed in Pa·s (pascal-seconds), mPa·s, or cP (centipoise), where 1 mPa·s = 1 cP. Kinematic viscosity is expressed in m²/s, mm²/s, or cSt (centistokes), where 1 mm²/s = 1 cSt.

Viscosity determines flow behavior in pipes, heat exchangers, pumps, and hydraulic systems. It directly affects pressure drop calculations, Reynolds number (laminar vs. turbulent flow), pumping power requirements, and heat transfer coefficients — making it critical for the design of water distribution networks, cooling systems, and industrial processes.