Water properties table
Density and viscosity of liquid water from freezing to boiling, at atmospheric pressure. These values feed flow, Reynolds number, and heat-transfer calculations, and they change noticeably with temperature.
Water at 1 atm
| Temp (°C) | Density (kg/m³) | Dyn. visc. (mPa·s) | Kin. visc. (mm²/s) |
|---|---|---|---|
| 0 | 999.8 | 1.792 | 1.792 |
| 10 | 999.7 | 1.307 | 1.307 |
| 20 | 998.2 | 1.002 | 1.004 |
| 30 | 995.6 | 0.798 | 0.801 |
| 40 | 992.2 | 0.653 | 0.658 |
| 50 | 988.0 | 0.547 | 0.554 |
| 60 | 983.2 | 0.467 | 0.475 |
| 70 | 977.8 | 0.404 | 0.413 |
| 80 | 971.8 | 0.355 | 0.365 |
| 90 | 965.3 | 0.315 | 0.326 |
| 100 | 958.4 | 0.282 | 0.294 |
Water density peaks near 4 degrees C at about 1000 kg/m3 and falls as it warms. Viscosity drops sharply with temperature: hot water at 80 degrees flows about five times more easily than cold water at 0. Dynamic viscosity is the resistance to shear; kinematic viscosity is that divided by density, and it is what enters the Reynolds number.
Working out a flow regime?
Use the kinematic viscosity here with the Reynolds Number Calculator or the Reynolds Number Flow Regimes chart.
Why viscosity matters for flow
Viscosity is the property that resists flow, and water loses much of it as it heats. That is why hot water pumps more easily and why warming a fluid can flip flow from laminar to turbulent. For Reynolds number and pressure-drop work, use the value at the operating temperature rather than a single room-temperature figure.
The density anomaly
Unlike most substances, water is densest as a liquid near 4 degrees C, not at freezing. Below that it expands again, and ice is less dense still, so ice floats. This quirk keeps lakes from freezing solid from the bottom up and matters whenever water near freezing is involved.
FAQ
What is the density of water?
About 1000 kg/m3 near 4 degrees C, falling to about 958 at the boiling point. It is commonly taken as 1000 for everyday work.
How does temperature affect water viscosity?
Viscosity falls sharply as water warms, from about 1.79 mPa-s at 0 degrees to 0.28 at 100, so hot water flows far more easily.
What viscosity do I use for Reynolds number?
The kinematic viscosity at the operating temperature, since Reynolds number is velocity times diameter divided by kinematic viscosity.