Keep the Mat & Frame Width in Proportion to the Image
Always consider the size of your painting or photograph when choosing the width of the frame. If the picture is large, then generally the frame width needs to be wide for the best look visually. If you are framing a large painting other options are a deep frame with a narrow edge or a floater frame. In any case, enough wood needs to be available to hold the physical weight as well as the visual look. The frame is hung from a wire held with hangers and screws. If the frame is too narrow because there isn’t enough wood, the screws will pull out due to the weight or break the wood. The screw size needs to match the weight of the piece.
You can also use the width of the mat and frame to simply imply scale. Increasing the width of the mat beyond a typical width is a way to add weight to a smaller photograph. Further, small and average-sized pictures can be elegant with a thin and lightweight frame taking into consideration the above.
The window cut in the mat for a photograph is typically smaller than the photograph. However, another idea with photography is to cut the window ¼ or ½ inch larger allowing some white space to show between the actual image and the beginning of the mat. In this case the photograph would be printed with a border of white.