Water Viscosity Calculator by Temperature

A water viscosity calculator using temperature estimates water’s dynamic viscosity from its temperature in degrees Celsius. Enter a temperature from 0 to 100 °C to get viscosity in pascal-seconds (Pa·s) and centipoise (cP), using an approximate correlation for liquid water near atmospheric pressure.

Formula

The calculator uses an empirical temperature correlation for liquid water:

μ = 2.414 × 10⁻⁵ × 10^{247.8 / (T + 133.15)}

• μ is dynamic viscosity in pascal-seconds (Pa·s).
• T is water temperature in degrees Celsius (°C).

Centipoise is a commonly used equivalent unit: 1 cP = 0.001 Pa·s, so cP = 1000 × μ. The correlation gives an estimate for ordinary liquid water; it is not a high-precision property table and does not account for pressure or dissolved substances.

Worked Example

For the default temperature, T = 20 °C:

1. Insert the temperature: μ = 2.414 × 10⁻⁵ × 10^{247.8 / (20 + 133.15)}.
2. Evaluate the exponent: 247.8 / 153.15 ≈ 1.6180.
3. Calculate viscosity: μ ≈ 2.414 × 10⁻⁵ × 10^1.6180 ≈ 0.001002 Pa·s.
4. Convert to centipoise: 0.001002 × 1000 ≈ 1.002 cP.

The calculator displays approximately 0.001002 Pa·s and 1.002 cP. Small differences in the last digit can occur because the equation is an approximation.

How Temperature Changes Water Viscosity

Viscosity describes a fluid’s resistance to flow. In liquid water, viscosity decreases as temperature rises: warmer water flows more readily, while colder water is more resistant to motion. At around 20 °C, water’s dynamic viscosity is close to 1.00 mPa·s, or 1.00 cP. Around 0 °C it is roughly 1.79 cP; near 100 °C it is about 0.28 cP at atmospheric pressure.

Those reference values help check whether a result is plausible. A temperature increase does not produce a linear decrease in viscosity, so multiplying or subtracting a fixed amount per degree is not a dependable substitute for a property correlation or table.

When to Use the Estimate

This calculator is useful for preliminary calculations involving liquid water, such as estimating Reynolds number, comparing flow resistance at two temperatures, or supplying a viscosity value to a basic fluid-flow calculation. It supplies dynamic viscosity only; other calculations may also require density, pipe dimensions, flow rate, or pressure conditions.

• Use the result as an estimate when water is reasonably pure and pressure is near atmospheric.
• For engineering work requiring tight tolerances, consult a recognized water-property table or a validated property model at the relevant temperature and pressure.
• For mixtures such as salt water, glycol solutions, or water containing substantial dissolved material, use properties for that actual mixture.

Temperature alone does not fully define a fluid’s properties in every situation. Pressure matters, especially near boiling conditions, and composition can change viscosity. The equation’s 0–100 °C input range is a practical limit for ordinary liquid-water estimates, not a claim that water remains liquid at every pressure throughout that interval.

Dynamic and Kinematic Viscosity

Do not confuse dynamic viscosity with kinematic viscosity. Dynamic viscosity, written μ, measures resistance to shear and is reported here in Pa·s or cP. Kinematic viscosity, written ν, is dynamic viscosity divided by density:

ν = μ / ρ

Here, ρ is density in kilograms per cubic metre (kg/m³), and ν is in square metres per second (m²/s). A common alternative unit for kinematic viscosity is the centistoke (cSt); 1 cSt = 1 mm²/s = 10⁻⁶ m²/s. To calculate ν, use a density appropriate to the same temperature and pressure. Dividing by a generic density can introduce error because water’s density also changes with temperature.

Units, Accuracy, and Common Mistakes

One pascal-second equals 1000 millipascal-seconds (mPa·s) and 1000 centipoise. For water near room temperature, 1 mPa·s and 1 cP are both convenient ways to express a value close to 1. This numerical equivalence does not mean the units are interchangeable in every conversion: keep track of the factor of 1000 between Pa·s and cP.

• Enter temperature in °C, not Fahrenheit. To convert Fahrenheit first, use °C = (°F − 32) × 5/9.
• Do not enter a Fahrenheit number directly. For example, 68 °F is 20 °C, not 68 °C.
• Keep dynamic and kinematic viscosity separate; they have different units and are not the same property.
• Do not report more precision than the temperature measurement or the correlation supports. Six displayed decimal places are a calculator format, not a guarantee of six-place accuracy.

The correlation is compact and practical, but its output should not be treated as a laboratory measurement. For high-accuracy work, use a source that specifies the measurement basis, temperature, pressure, and water composition.

Frequently Asked Questions

What is the viscosity of water at 20 °C?
It is about 0.001002 Pa·s, equivalent to approximately 1.002 cP, using the correlation in this calculator. Tabulated values may differ slightly depending on precision and conditions.

Does water viscosity increase or decrease with temperature?
For liquid water, viscosity generally decreases as temperature rises. This is why warmer water flows more easily than colder water under otherwise similar conditions.

Can I enter Fahrenheit into the calculator?
No. The input is Celsius. Convert first with °C = (°F − 32) × 5/9; for example, 68 °F equals 20 °C.

Is cP the same as mPa·s?
Yes. One centipoise equals one millipascal-second: 1 cP = 1 mPa·s. Both equal 0.001 Pa·s.

Can this calculate viscosity for seawater or antifreeze?
Not accurately. The formula estimates ordinary liquid water and does not include the effects of salt, glycol, or other dissolved substances. Use a property source for the specific mixture.

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in t | Water temperature | °C | 20 | 0 | 100
out mu | Dynamic viscosity | Pa·s | 2.414e-5 * 10^(247.8 / (t + 133.15)) | 6
out cp | Dynamic viscosity | cP | mu * 1000 | 3