The Collaborative International Dictionary of English v.0.48:

magnetic field strength \magnetic field strength\ n.
   The amount of magnetic flux in a unit area perpendicular to
   the direction of magnetic flow.

   Syn: magnetic intensity, magnetic induction, magnetic flux
        density.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

magnetic field strength
    n 1: the amount of magnetic flux in a unit area perpendicular to
         the direction of magnetic flow [syn: magnetic field
         strength, magnetic intensity, magnetic induction,
         magnetic flux density]