Gas Viscosity Calculator

Example Data Table

Sample runs to illustrate how temperature changes viscosity. Values are examples for demonstration, not a substitute for validated property data.

Formula Used

This calculator uses a Sutherland-type correlation to estimate dynamic viscosity as a function of absolute temperature:

• μ: dynamic viscosity at temperature T (cP in this correlation)
• μ₀: reference viscosity at T₀ (cP)
• T, T₀: absolute temperature (°R for this parameter set)
• C: Sutherland constant for the gas

Conversions: 1 cP = 1 mPa·s = 0.001 Pa·s.

How to Use This Calculator

1. Select Common gas to use preset parameters, or choose Custom for your own μ₀, T₀, and C.
2. Enter the temperature and pick the correct unit. Absolute units (K or °R) are best for high accuracy.
3. Optionally enter density to compute kinematic viscosity (ν = μ/ρ).
4. Press Submit. Results appear above the form under the header.
5. Use Download CSV or Download PDF to save the report.

Temperature drives molecular momentum transfer

Gas viscosity rises with temperature because faster molecules exchange momentum more effectively. In the calculator, temperature is converted to an absolute scale before evaluation, which prevents negative or zero absolute values from corrupting the correlation. For air near room conditions, typical dynamic viscosity is around 1.8×10⁻⁵ Pa·s and increases by roughly 15–25% by 100°C. Use absolute units when operating far from ambient conditions. Record the temperature basis in your calculation notes under expected operating conditions.

Using Sutherland parameters for common gases

The model applies a Sutherland-type correlation with a reference viscosity μ0 at reference temperature T0 and an empirical constant C. Preset gases provide tuned parameter sets that are suitable for quick engineering estimates when composition is known. If your process gas is a mixture or contains humidity, select Custom and use published property data for μ0, T0, and C matching your specification and temperature band. Update parameters when standards or datasheets change.

Interpreting units and outputs in practice

Results are presented as dynamic viscosity in both Pa·s and cP (equal to mPa·s). This dual output helps bridge SI calculations and legacy specifications in datasheets, pumps, and instrumentation. The table repeats the input temperature, its absolute equivalents, and the parameter values used, so the record is auditable. When exporting, keep the reported units with each value to avoid misapplication in downstream models. Include the selected method in your reports for traceability.

Adding density to obtain kinematic viscosity

Many flow calculations use kinematic viscosity ν, especially when Reynolds number and friction factors are required. If you provide density, the calculator computes ν = μ/ρ in m²/s. This is useful for CFD pre-processing, pipe sizing, and valve Cv checks where viscosity and density jointly influence losses. Enter density at the same temperature and pressure as the viscosity estimate to maintain consistency. If density is uncertain, run a sensitivity range.

Engineering checks and limitations

Sutherland correlations are most reliable for dilute gases at low-to-moderate pressures, away from critical regions. At very high pressures, strong real-gas effects can shift transport properties, and specialized correlations or experimental data may be needed. Treat the result as an estimate, then compare against trusted databases or vendor curves. For safety-critical design, document the chosen parameter source and validate the operating range. Re-check units, rounding, and input plausibility before final signoff.

FAQs

1) Why does gas viscosity increase when temperature rises?

Higher temperature increases molecular speeds and momentum exchange, raising resistance to shear. The correlation captures this trend by using absolute temperature in a power term and a temperature-dependent correction factor.

2) When should I use the Custom parameter option?

Use Custom when your gas is not listed, when composition differs from “standard” assumptions, or when you have vendor or database reference values. Match μ0, T0, and C to your intended temperature range.

3) What density should I enter for kinematic viscosity?

Enter density at the same temperature and pressure as the viscosity estimate. If density comes from an equation of state or datasheet, ensure it reflects operating conditions rather than standard reference conditions.

4) Are pressure effects on viscosity ignored here?

The method primarily models temperature dependence and is best for dilute gases at moderate pressures. At high pressures or near critical regions, consider real-gas transport models or validated experimental property data.

5) How accurate are the preset gas parameters?

They are intended for fast engineering estimates and reasonable temperatures, not guaranteed for all conditions. For design-critical work, compare results against a trusted property source and document the parameter set used.

6) Which unit should I use for reporting viscosity?

Use Pa·s for SI workflows and cP (mPa·s) when matching common equipment datasheets. Always include units in exports and reports to prevent conversion mistakes across teams and tools.