What this calculator does
This water viscosity calculator works out how resistant water is to flowing at a given temperature, reporting both dynamic viscosity and kinematic viscosity. The viscosity of water at 20°C is about 1.002 millipascal-seconds, but it changes substantially across the temperature range liquid water can exist at, which is why temperature is the only input this calculator needs.
Viscosity is a different physical property from density, which this site's separate water density calculator covers. Density measures mass per unit volume; viscosity measures resistance to flow. Both change with temperature, but not in the same proportion, so a fluid can get noticeably less viscous while its density barely moves.
The formula
Dynamic viscosity is calculated from a standard temperature-dependent correlation (Kestin, Sokolov & Wakeham, 1978), referenced to a value of 1.002 mPa·s at 20°C and valid across the 0°C to 100°C liquid range at standard atmospheric pressure. Kinematic viscosity is then found by dividing dynamic viscosity by water's density at that same temperature, using the same density relationship as this site's water density calculator.
| Term | Meaning |
|---|---|
| Dynamic viscosity (μ) | A measure of a fluid's internal resistance to flow, in millipascal-seconds (mPa·s), numerically equal to centipoise (cP). |
| Kinematic viscosity (ν) | Dynamic viscosity divided by density, in square millimetres per second (mm²/s), numerically equal to centistokes (cSt). |
| mPa·s / cP | Millipascal-second and centipoise are two names for the same unit of dynamic viscosity, both still in common use. |
The inputs explained
| Field | What to enter |
|---|---|
| Water temperature (°C) | The water temperature in degrees Celsius, anywhere from 0°C to 100°C. |
When to use it
Sizing a pump or pipe
Pump and pipe flow calculations depend on the viscosity of the fluid being moved, and water's viscosity at an elevated operating temperature is noticeably lower than at room temperature.
Comparing dynamic and kinematic viscosity
Some engineering references and equipment specifications use dynamic viscosity, others use kinematic; having both figures for the same temperature avoids a unit mismatch when cross-checking a spec sheet.
Understanding why warm water feels thinner
The drop in viscosity as temperature rises is the physical reason warm water pours and drains noticeably faster than cold water, well before it is anywhere near boiling.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the viscosity of water changes with temperature
Water viscosity across its full liquid temperature range at standard atmospheric pressure.
| Temperature | Dynamic viscosity | Kinematic viscosity |
|---|---|---|
| 0°C | 1.792 mPa·s (cP) | 1.792 mm²/s (cSt) |
| 10°C | 1.307 mPa·s (cP) | 1.307 mm²/s (cSt) |
| 20°C | 1.002 mPa·s (cP) | 1.004 mm²/s (cSt) |
| 25°C | 0.8902 mPa·s (cP) | 0.8928 mm²/s (cSt) |
| 37°C | 0.6913 mPa·s (cP) | 0.6959 mm²/s (cSt) |
| 50°C | 0.5462 mPa·s (cP) | 0.5528 mm²/s (cSt) |
| 75°C | 0.3745 mPa·s (cP) | 0.3841 mm²/s (cSt) |
| 100°C | 0.2733 mPa·s (cP) | 0.2851 mm²/s (cSt) |
Questions
What is the viscosity of water at room temperature?
At 20°C, water has a dynamic viscosity of about 1.002 mPa·s and a kinematic viscosity of about 1.004 mm²/s. At the slightly warmer 25°C sometimes used as a lab reference, dynamic viscosity drops to about 0.890 mPa·s.
What is the difference between dynamic and kinematic viscosity?
Dynamic viscosity measures resistance to flow under an applied force, independent of density. Kinematic viscosity divides that figure by density, which is useful because it appears directly in many fluid-flow equations, such as those used for pipe flow and Reynolds number.
Why does viscosity fall as temperature rises, while density only falls slightly?
Viscosity in a liquid comes mainly from molecules briefly bonding to their neighbours as they try to slide past each other; heat disrupts those bonds strongly. Density depends on how tightly packed the molecules are overall, which heat affects far less over the same temperature range.
Does this calculator account for salt content or pressure?
No. This is a pure-water correlation at standard atmospheric pressure. Dissolved salts, as in seawater, and significantly elevated pressure both change viscosity slightly from these figures.
For the density figures used in the kinematic viscosity conversion, see the water density calculator. For flow calculations that use these viscosity or density figures directly, see the flow rate calculator.