Why does water viscosity decrease with temperature?

In liquids, viscosity arises from intermolecular cohesive forces. Higher temperature gives molecules more kinetic energy to overcome these forces, reducing resistance to flow.

What units is viscosity measured in?

SI unit of dynamic viscosity is Pa·s. The CGS unit poise (P) = 0.1 Pa·s; centipoise (cP) = 1 mPa·s. Water at 20°C is almost exactly 1 cP, which historically defined the centipoise.

What is the difference between dynamic and kinematic viscosity?

Dynamic viscosity μ (Pa·s) is the shear-stress-to-strain-rate ratio. Kinematic viscosity ν = μ/ρ (m²/s) divides out the density, representing the diffusion of momentum. ν appears in the Reynolds number.

How does pressure affect water viscosity?

At pressures below about 100 bar, the effect is negligible (< 2%). At very high pressures (e.g., deep ocean), viscosity increases measurably. This calculator assumes atmospheric pressure.

What is the Prandtl number and why does it matter?

Pr = ν/α = μ c_p / k compares momentum diffusion to thermal diffusion. For water, Pr ranges from 13.4 at 0°C to 1.76 at 100°C. High Pr means the thermal boundary layer is thinner than the velocity boundary layer.

Can I use these values for saltwater?

Seawater at 35 g/kg salinity is about 8% more viscous than freshwater at the same temperature. Apply a correction factor or use specific seawater property tables.

Water Viscosity Calculator

Calculate dynamic viscosity, kinematic viscosity, density, and thermal properties of water at any temperature from 0–100 °C.

Water temperature

Unit

Dynamic Viscosity (μ)

1.0017 mPa·s

1,001.75 × 10⁻⁶ Pa·s — also 1 mPa·s = 1 cP

Kinematic Viscosity (ν)

0.7503 × 10⁻⁶ m²/s

0.7503 cSt

Density (ρ)

1,335.20 kg/m³

Max at ~4°C: 999.97 kg/m³

Surface Tension (σ)

72.87 mN/m

Water–air interface

Specific Heat (c_p)

4,151.0 J/(kg·K)

At 1 atm

Thermal Conductivity (k)

0.5993 W/(m·K)

Liquid phase

Prandtl Number (Pr)

6.94

Pr = μ c_p / k

Viscosity vs Temperature

0°

5°

10°

15°

20°

25°

30°

35°

40°

50°

60°

70°

80°

90°

100°

Temperature (°C) — viscosity drops sharply with heat

T (°C)	μ (mPa·s)	ν (×10⁻⁶ m²/s)	ρ (kg/m³)	Pr
0	1.753	1.753	999.8	13.12
5	1.501	1.384	1,084.4	11.00
10	1.300	1.112	1,168.4	9.34
15	1.136	0.907	1,252.1	8.01
20	1.002	0.750	1,335.2	6.94
25	0.890	0.628	1,417.8	6.07
30	0.797	0.532	1,499.8	5.35
35	0.718	0.454	1,581.3	4.75
40	0.651	0.392	1,662.2	4.25
50	0.544	0.299	1,821.9	3.46
60	0.463	0.234	1,979.0	2.89
70	0.400	0.188	2,133.1	2.45
80	0.351	0.154	2,284.1	2.12
90	0.311	0.128	2,431.8	1.86
100	0.279	0.108	2,576.1	1.66

Planning notes, formulas, and examples

About the Water Viscosity Calculator

Water viscosity is one of the most frequently looked-up fluid properties in engineering. Dynamic viscosity μ drops dramatically with temperature — from about 1.79 mPa·s at 0°C to 0.28 mPa·s at 100°C — a six-fold decrease that profoundly affects flow behaviour, heat transfer, and pump performance.

This calculator uses the Vogel–Tammann–Fulcher correlation for dynamic viscosity and standard polynomial fits for density, thermal conductivity, specific heat, and surface tension. It outputs seven key properties: μ, ν, ρ, σ, c_p, k, and the Prandtl number. These are the essential inputs for Reynolds number, Nusselt number, and nearly every fluid-mechanics and heat-transfer correlation.

A visual bar chart shows how viscosity plummets with temperature, while the reference table gives values at 5°C intervals from 0°C to 100°C. Temperature presets include body temperature (37°C) for biomedical applications and other common engineering setpoints. That makes the page useful both as a lookup table and as a quick source for coupled fluid-property calculations at operating temperature.

When This Page Helps

Use this reference when you need temperature-dependent water properties for Reynolds number, pump sizing, pressure-drop estimates, or heat-transfer calculations without switching between multiple tables. It is especially useful when viscosity, density, and Prandtl number all need to stay synchronized at the same temperature in one calculation chain. That keeps the fluid-property inputs consistent when one operating temperature feeds several downstream calculations.

How to Use the Inputs

Enter the water temperature in °C, °F, or K.
Use a temperature preset for common conditions.
Read dynamic viscosity (μ), kinematic viscosity (ν), density, and more from the outputs.
Check the Prandtl number for heat-transfer calculations.
Consult the full property table for values at multiple temperatures.
Use the viscosity chart to visualize the temperature dependence.

Formula used

Dynamic viscosity: μ = A × 10^(B / (T − C))
  A = 2.414×10⁻⁵, B = 247.8, C = 140  (T in Kelvin)

Kinematic viscosity: ν = μ / ρ
Prandtl number: Pr = μ c_p / k

ρ, c_p, k, σ: standard polynomial correlations for 0–100°C

Example Calculation

Result: μ = 1.002 mPa·s, ν = 1.004 × 10⁻⁶ m²/s

At 20°C (293.15 K), the VTF formula gives μ = 2.414e-5 × 10^(247.8/(293.15−140)) ≈ 1.002e-3 Pa·s. With ρ = 998.2 kg/m³, ν = 1.002e-3/998.2 = 1.004e-6 m²/s.

Tips & Best Practices

At exactly 20.2°C, water viscosity is 1.000 mPa·s (1 cP) — a handy reference point.
Water density peaks near 4°C (999.97 kg/m³), which is why ice floats.
For pipe-flow calculations, always use viscosity at the operating temperature — summer vs winter water can differ by a factor of 2.
The Prandtl number of water drops from ~13 at 0°C to ~1.8 at 100°C, dramatically affecting heat-transfer coefficients.
Viscosity of water–glycol mixtures can be orders of magnitude higher than pure water.

Why Temperature Matters

Water viscosity changes quickly with temperature, which means the same pipe, pump, or heat exchanger can behave very differently between cold-start and operating conditions. A design that looks acceptable at 20°C may produce very different pressure losses at 5°C or 80°C.

Using The Output

Dynamic viscosity is the quantity you need for shear-stress and constitutive relations, while kinematic viscosity is usually the value used in Reynolds number and many empirical flow correlations. If you are checking convective heat transfer, pair viscosity with thermal conductivity, specific heat, and Prandtl number rather than looking at viscosity in isolation.

Limits To Remember

These values are intended for liquid water near atmospheric pressure over the stated temperature range. They are not a substitute for steam tables, high-pressure property databases, or saline-water correlations.

Sources & Methodology

Last updated: March 26, 2026

Methodology

This calculator converts the submitted temperature to degrees Celsius, restricts the range to liquid water from 0 °C to 100 °C, and then applies the Vogel–Tammann–Fulcher correlation μ = 2.414 × 10⁻⁵ × 10^(247.8 / (T − 140)) with T in kelvin to estimate dynamic viscosity.

Kinematic viscosity is computed as ν = μ / ρ. Density, surface tension, specific heat, and thermal conductivity are estimated from the polynomial fits implemented in the calculator so the reported properties remain internally consistent at the same temperature. The Prandtl number is calculated as Pr = μ c_p / k.

These results are intended for near-atmospheric liquid-water estimates. They are not a substitute for high-pressure steam-table work or saline-water property data.

Sources

NIST Chemistry WebBook, SRD 69: Thermophysical Properties of Fluid Systems (NIST)
NIST Chemistry WebBook: Water (NIST) — Reference page for water and linked thermophysical data.

Frequently Asked Questions

In liquids, viscosity arises from intermolecular cohesive forces. Higher temperature gives molecules more kinetic energy to overcome these forces, reducing resistance to flow.