Air properties calculator
Not sure where to start? 4 places to go
Start with your question
Why visitors arrive: You need dry-air density, viscosity, or conductivity at a temperature for CFD, similarity, or lab sizing.
Your question: What are air properties at my temperature and pressure, and which correlations are used?
You may also be asking
- How do I check Reynolds or Mach with these values?
- Where is this used in published work?
- What about pipe flow or heat-exchanger sizing?
Where to go next
- Dimensionless groups reference: Similarity checks after you have properties
- Dimensional analysis module: Pi-group scaling theory
- CFD-experiment validation article: Pairing simulation BCs with data
- All calculators: Other tools on the platform
Lucas Rey: aerothermal engineer · ORCID · About · Publications
Interactive utility for the thermophysical characterization of dry air. Computes density, viscosity, thermal conductivity, specific heats, and Prandtl number from validated aerothermal correlations, part of the engineering calculators on the knowledge platform.
Air properties calculator
Compute temperature-dependent thermophysical properties of dry air. Optionally include pressure to obtain density, thermal diffusivity and kinematic viscosity.
What the calculator returns
Enter one air temperature, in K, °C or °F, and the tool returns eight properties. Tick the pressure box and it returns three more, because density, kinematic viscosity and thermal diffusivity all need a pressure as well as a temperature. Every result has a copy button, and the set can be downloaded as a text file.
- Thermal conductivity of air, k: in W/(m·K). This is the quantity usually meant by the k value of air
- Dynamic viscosity, µ: in kg/(m·s), which is the same unit as Pa·s. Divide by 0.001 for centipoise
- Specific heat at constant pressure, cp, and at constant volume, cv: in J/(kg·K)
- Ratio of specific heats, γ = cp/cv: dimensionless, and written k in some thermodynamics and compressible flow texts
- Prandtl number, Pr = cpµ/k: dimensionless
- Specific enthalpy, h: in J/kg, taken relative to 0 °C
- Density, ρ: in kg/m³, from the ideal gas law. Needs the pressure box
- Kinematic viscosity, ν = µ/ρ: in m²/s. Needs the pressure box
- Thermal diffusivity, α = k/(ρcp): in m²/s. Needs the pressure box
Which k did you mean
Two different quantities are written k, and the tool gives you both from the same temperature, so you do not have to decide in advance. In heat transfer, k is the thermal conductivity: for dry air at 25 °C this calculator returns 0.02606 W/(m·K). In thermodynamics and compressible flow, k is often written for the ratio of specific heats, cp/cv, which is 1.40206 for dry air at the same temperature and appears here as γ.
Correlations & valid range
The calculator evaluates dry-air properties using piecewise correlations suited to aerothermal and gas-turbine temperature bands. Density follows the ideal-gas law with a temperature-dependent gas constant treatment appropriate for the stated range; viscosity and thermal conductivity use standard engineering correlations for air; specific heats and Prandtl number are derived consistently from those inputs.
- Temperature range: 200 K, 2000 K (dry air, near-atmospheric applications as used in rig sizing)
- Assumption: Dry air, moisture effects are not modelled; humid flows require separate property treatment
- Outputs: Density, dynamic viscosity, thermal conductivity, specific heat at constant pressure, and Prandtl number in SI units
- Traceability: Use documented inputs when coupling to CFD-experiment validation or experimental measurement workflows, similarity arguments fail when property tables are inconsistent between solver and experiment
Typical uses on this site
Reynolds & Prandtl sizing
Estimate Re and Pr for channel or probe similarity checks before running the viscous flow problem sets or scaling a wind-tunnel model.
Boundary conditions
Supply consistent thermophysical inputs when documenting CFD boundary conditions, see the CFD-experiment validation article for how properties enter validation statements.
Facility checks
Cross-check rig operating points against published campaigns on projects and turbomachinery deterioration research.
Related on this site
- Calculators hub: index of interactive engineering tools
- Fluid mechanics curriculum: Pi groups, viscous flow, and similarity modules
- Viscous flow problems: pipe-flow exercises that use thermophysical inputs
- Dimensional analysis: Pi groups and similarity scaling
- Experimental aerothermal measurement: methods article on traceability and facility transfer
- CFD-experiment validation: closing the loop between simulation and measurement
- Instrumentation & measurement: experimental methods theme
- Publications: research using aerothermal property correlations
- Engineering hub: full platform index
A hard R&D problem is the kind of conversation I enjoy most, and most of my work has started as one.
Part of
This page sits within the broader knowledge structure on lucasrey.com:
- Engineering - Central knowledge platform - tools, curriculum, notes, and research assets.
- Tools - Interactive calculators and engineering utilities.
Connected work
Related content from the same research and engineering work:
- Calculators hub
- Viscous flow problems
- Dimensional analysis
- Curriculum index
- Air properties calculator - Referenced from HPT transient thermography
- Air properties calculator - Referenced from Turbomachinery deterioration
- Air properties calculator - Referenced from Thermal & additive design
Part of Engineering
This page is part of the engineering knowledge platform on lucasrey.com.
- Engineering hub - Full knowledge platform index
- Engineering calculators - Air properties and pipe flow (live); probe uncertainty and heat-exchanger screening (planned).
- Pipe flow calculator - Reynolds number, Colebrook friction factor, Darcy-Weisbach pressure drop, head loss and wall shear stress for a full circular pipe.
- Engineering calculators - Air properties and pipe flow (live); probe uncertainty and heat-exchanger screening (planned).
- Fluid mechanics curriculum - Index and learning path across modules.
- Dimensional analysis - Pi groups, similarity, and model testing.
- Viscous flow - problems - Worked and practice problems for viscous flow.
- Instrumentation & measurement - Pneumatic probing, calibration transfer, and uncertainty propagation.
- Experimental aerothermal measurement - Methods article on traceability, similarity, and facility transfer - links instrumentation, curriculum, and tools.
- CFD-experiment validation - Methods article on closing the loop between RANS simulations and transient aerothermal measurements.
- Publications - Peer-reviewed papers and manuscripts in preparation - research pillar with thematic hubs, project links, and structured metadata.
- Calculators hub
- Viscous flow problems
- Dimensional analysis
Engineering knowledge platform
More tools, curriculum, notes, and research from the same body of work:
- Engineering - Central knowledge platform - tools, curriculum, notes, research, and applied engineering work.
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