A critical requirement for bit patterned media applications is the control and minimization of the switching field distribution (SFD). Here, we use the ΔH(M,ΔM) method to separate dipolar interactions due to neighbor islands from the intrinsic SFD by measuring a series of partial reversal curves of perpendicular anisotropy Co/Pd based multilayer films deposited onto prepatterned Si substrates. For a 100-nm-period island array the dipolar broadening contributes 22% to the observed SFD. For a 45-nm-period array this value increases to 31%. These results highlight the importance of quantifying long-range dipolar interactions for determining the intrinsic SFD of patterned media.