Encyclopedia of dimensionless numbers#

Dimensionless numbers appear throughout science and engineering whenever a physical phenomenon can be characterised by the ratio of two competing effects — inertia versus viscosity, convection versus conduction, oscillation versus transport. Because they carry no units, the same number describes the same physical balance regardless of the scale or the working fluid, making them the natural language of similarity, scaling, and dimensional analysis.

Current database

For each number you will find its definition as a ratio of named physical quantities, the physical interpretation of numerator and denominator, the dimensions of every quantity involved, and - where applicable - the flow regimes the number delineates. Each quantity links back to the numbers that use it.

Explore all numbers, look up individual quantities, or read more about the database.

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