Blocking temperature (TB) of a fine particle system is found to vary with external field H, dipole interaction and magnetic configuration of the system. The TB distribution curve evaluated at H ≃ 0 agrees well with the weighted volume distribution of the system and only the field-cooled magnetization (MFC) alone is relevant. The behavior of MFC and MZFC curves depends sensitively on H compared to dipole interaction. Both TB and the volume distribution of the system can be deduced directly if MFC variation with temperature is measured.