A new equation for the convective heat loss from the sensor of a hot-wire probe is derived which accounts
for both the potential and the viscous parts of the ow past the prongs. The convective heat loss from the
sensor is related to the far- eld velocity by an expression containing a term representing the potential ow
around the prongs, and a term representing their viscous e ect. This latter term is absent in the response
equations available in the literature but is essential in representing some features of the observed response
of miniature hot-wire probes. The response equation contains only four parameters but it can reproduce,
with great accuracy, the behaviour of commonly used single-wire probes. The response equation simpli es
the calibration the angular response of rotated slanted hot-wire probes: only standard King's law parameters
and a Reynolds-dependent drag coefficient need to be determined.