Water Viscosity Calculator
Water’s resistance to shear decreases strongly as temperature rises. This calculator estimates the dynamic viscosity of liquid water at the entered Celsius temperature and reports millipascal-seconds (mPa·s). One mPa·s equals one centipoise (cP).
The implementation uses a temperature correlation published in NIST’s Journal of Physical and Chemical Reference Data. It is designed for liquid water over the source’s stated range, not for ice, steam, salt water, or an arbitrary aqueous mixture.
Method
The correlation expresses viscosity relative to the 20°C reference value. Let x = 20 − t, with t in °C. The calculator evaluates:
log₁₀[μ(t) ÷ μ(20°C)] = x × [1.2378 − 0.001303x + 0.00000306x² + 0.0000000255x³] ÷ (96 + t)
It then multiplies the ratio by the reference viscosity, 1.002 mPa·s at 20°C. Inputs outside −8°C to 150°C are rejected rather than extrapolated.
Worked example
At t = 100°C, x = −80. Substituting those values gives a ratio of about 0.2815. Multiplying by the 20°C reference yields approximately 0.282 mPa·s at 100°C.
At 20°C the exponent is zero, the ratio is one, and the calculator returns 1.002 mPa·s. These two checkpoints are included in the automated regression tests.
What the result means
Dynamic viscosity relates shear stress to the rate of deformation in a Newtonian fluid. Lower viscosity means the liquid offers less viscous resistance under the same shear conditions. This property is used in Reynolds-number estimates, pressure-loss models, pump calculations, laboratory corrections, and heat-transfer work.
Dynamic viscosity is not kinematic viscosity. Kinematic viscosity equals dynamic viscosity divided by density and is expressed in m²/s or a related unit. Do not substitute one for the other without the density and unit conversion.
Accuracy and limitations
The formula represents pure liquid water and is primarily temperature dependent at ordinary pressures. Dissolved salts, sugars, glycols, suspended material, impurities, and high pressure can change viscosity. Near phase boundaries, confirm that the selected pressure keeps water liquid; entering 100°C does not by itself specify whether the sample is liquid.
The displayed digits do not imply equal experimental accuracy. Use an applicable reference formulation or measured property data for custody transfer, calibration, high-pressure design, pharmaceutical work, or safety-critical engineering.
Sources
- NIST, “Viscosity of Liquid Water in the Range −8°C to 150°C” — source range, reference values, and temperature correlation.
- NIST, “Tables of the Dynamic and Kinematic Viscosity of Aqueous Solutions” — confirms the 20°C water reference and distinguishes dynamic and kinematic properties.
Editorial record
Written and formula-checked by the SoupCalc Editorial Team. Reference cases at 20°C and 100°C, range rejection, and output units were tested against the cited correlation.
Last reviewed: August 10, 2026.