The Eckert number (Ec) is a dimensionless number used in continuum mechanics. It expresses the relationship between a flow's kinetic energy and the boundary layer enthalpy difference, and is used to characterize heat dissipation. It is named after Ernst R. G. Eckert.
It is defined as

where
- u is the local flow velocity of the continuum,
- cp is the constant-pressure local specific heat of the continuum,
is the difference between wall temperature and local temperature.