If the ceilings are high, you might look at the heavy framed mirrors that will be in keeping with the other moldings in the room.
If the ceilings are low, a narrow mirrors profile that delicately frames the glass might be your choice.
The same scale relationship is true of space between windows.
If a framed mirrors almost filling the space – it might be the full height of the windows, but held back mirrors enough from each side to accommodate curtains – it will emphasize the vertical nature of the room and make the space between the windows as visually active as the windows on either side.
In a nineteenth-century room, the overmantel mirrors or pier glass mirrors would be framed in a decorative motif, either in wood or plaster, but it would fill the available surface as high and broad as can be.
To create an overmantel mirror, you may decide to mirror the whole wall, or you may simply choose a frame for the mirror that fills as much of the space over the mantel as possible and have a mirror made. Both techniques will draw attention to the fireplace, host to the biggest seating group in the case of a living room, but the second offers more decorative options.
Mirrors in a bathroom usually located above the sink, and should be big and functional. Height of the bathroom mirrors has to be at least one-fourth of your body height.