Determining the proper mat size opening for a print can be a little confusing. One simple rule is that the mat opening should not be the same size as the print or photo. They will not be exactly the same size and it is nearly impossible to get them lined up perfectly. Off the shelf picture frames usually have mat board openings 1/2 inch smaller. For example if you purchase a 16×20 inch frame for 11×14 prints the actual opening in the matboard will usually be 10 1/2 x 13 ½ inches. This results in the mat overlapping each side of the print by 1/4. Personally I consider that too much so Frame Destination mats are cut ¼” smaller which allows for just 1/8” overlap of each side except for prints larger than 18×24. When the mat overlaps the print you do not have to worry about the color of any paper border around the image or the color of the substrate the image is mounted to. The mat board will also help keep the image flat.
Although allowing the mat to overlap the image is the most common matting technique, another option is to use a mat opening that is larger than the image. This matting technique will prevent the image being masked and allows for a signature to be visible below the image. Usually the side and top borders are between 1/4 to 1/2 inch and the bottom is between 1/4 and 1 inch. The bottom will usually be equal to the top and sides unless there is a signature. For example if the signature is under 1/2 inch then you can use 1/4 or 3/8 inch top and side borders and 1/2 inch bottom border. If the signature requires 3/4 inch then you can use 1/2 top and side borders. In this case the mat opening will be 1 inch larger than the image width, and 1 1/4 inches larger than the image height. A common mistake is to forget to double the border size when calculating the opening.
Frame Destination, Inc.