How this calculator works
Prandtl number compares the rates at which momentum and heat diffuse through a fluid. Large values mean momentum diffuses more rapidly than heat; small values mean heat diffuses more rapidly. Use specific heat at constant pressure and consistent fluid properties. Density cancels from Pr itself but is needed to report both diffusivities. The water reference is a rounded NIST-property example near 20 C and 1 bar; other fluids and temperatures require custom data.
Formula
Pr = nu/alpha = mu cp/k. Momentum diffusivity nu = mu/rho. Thermal diffusivity alpha = k/(rho cp). These diffusivities have units m2/s.
Worked example
For mu = 0.001 Pa s, cp = 4000 J/(kg K) and k = 0.5 W/(m K), Pr = 8. If nu = 1e-6 m2/s and alpha = 2e-7 m2/s, Pr = 5.
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Frequently asked questions
Is Prandtl number dimensionless?
Yes. In a consistent unit system the units of viscosity times heat capacity cancel those of thermal conductivity.
Does density affect Pr?
It cancels in the ratio of momentum to thermal diffusivity. It still affects the individual diffusivities.
Can I mix properties from different temperatures?
No. That combination may not describe any real fluid state and can give a misleading Prandtl number.