in an electric field is given by 
where
is typically arranged to be of the order of 
.
In the presence of a magnetic field B, the drift velocity is reduced, and the drift direction is no longer along the electric field.
The apparent drift velocity is
where 
is the drift angle given by
This assumes B and E to be orthogonal. For details, see [Sauli91]. More general formulae are given in [Blum93].