Sometimes a unit will contain creatures with different Toughness characteristics. When this is the case allocate hits before rolling to wound. You may only allocate one hit against each model until all of the models in the unit have taken one hit each.
Diagram: Allocating Hits. A unit of Space Marines shoots and scores four hits at a mixed Ork unit containing an Ork Nob, two Orks, and two Gretchin. The Ork player allocates three hits to the Gretchin (T2) and one to an Ork (T4) before his opponent rolls to wound.