Decorating over a fire place

When picking the appropriate demension for your family portrait  (or any artwork) to go over a fire place it should be equal or greater than the opening of the fireplace.  Aside from the few times a fireplace is lit The fireplace is a large black space so whatever you display above it needs to balance or be greater than the fireplace or else it will overwhelm

the wall and distract from the art piece above it.