Proper Mat Size for Matting an Image

Framing involves many different aspects. Determining the proper mat size and mat opening for a print or photograph is one of the more confusing issues facing novice framers.

First, be sure you understand the two different measurements associated with a frame mat. There is the overall size of the mat, which is around the size of the inside of the frame. Then, there is the mat window measurement, which refers to the size of the opening in the mat through which the image shows.

Measure the Dimensions

To determine the general overall dimensions of the mat, measure the size of the glazing of the intended frame. If the glass fits well inside the frame without too much wiggle room, it provides a good template for cutting the mat to its overall size. There is some room for error in cutting, since part of the frame will conceal smaller irregularities, but keep in mind there is about a 1/8” margin of error before you start noticing imperfections in the framing job.

As for the size of the window in the mat, one simple general rule is that the opening should not be the same size as the print or photo. Cutting a mat to the exact dimensions of the outer border of a picture or photograph is almost impossible and it is nearly impossible to get them lined up perfectly.

Off- the- shelf pre-cut picture frames usually have mat boards with openings 1/2 an inch smaller than the intended picture size. For example, a 16×20 inch frame including a mat purchased for use with 11×14 prints or photographs will have an actual window opening somewhere in the neighborhood of 10 1/2 x 13 ½ inches. This results in the mat overlapping each side of the print by ¼ inch. A quarter of an inch does not sound like much on its own, but consider that it adds up since there are four sides on every mat.

Matting Techniques

float mountingAlthough allowing the mat to overlap the image is the most common matting technique, sometimes employing the practice of using a mat opening that is larger than the image, known as “float mounting”, works best. This matting technique prevents any masking of any part of the framed image. It is especially useful when the ability to view the artist’s signature or print data is desired.

There are several ways to accomplish this look, including using different overlap measurements on different edges of the work. Usually the side and top border measurements are between 1/4 to 1/2 inch and the bottom is expanded to reveal between 1/4 and 1 inch of the border. In most cases, the bottom dimensions of a mat are equal to the top and sides, but the presence of a signature changes all that. However, getting it right requires a little math along with some good measuring skills. Beyond that, another common mistake is to forget to double the border size when calculating the opening.

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 one inch larger than the image width, and 1 1/4 inches larger than the image height.

Sometimes drawing out a sketch prior to making any cuts helps better visualize your aims. Beyond that, never forget that the adage, “measure twice, cut once” does not just apply to woodworking.

Mats are integral parts of framing. Their color accents the framed item, setting it off to its best effect. Their composition ensures preservation of the item. However, mats serve other purposes. They provide a buffer layer between the artwork or photo and the frame glazing. Beyond that, the mat board helps keep the framed image flat within the frame, and adds another way to create a truly distinctive and unique framed look.

Frame Destination carries several varieties of mats, including 100% cotton, acid-free and lignin-free mats with solid color throughout, mats that trap and neutralize pollutants and acid by-products, and paper mat featuring white or cream cores. All mats from our shop feature larger windows than most store-bought mats, meaning more of the image showing through in a framed piece. All artwork below 20” on each side has mat windows cut ¼ of an inch smaller, which allows for just 1/8 of an inch overlap for each side. Opening for images 20” and larger on both sides are cut ½” smaller. The slightly enlarged cut out window still allows for sufficient coverage or overlap of any paper border around the image, thereby supporting the image, and negating any concerns about the color of the substrate the image is mounted against showing up in the completed framed item.

About the author


Mark Rogers is an amateur photographer and the founder of Frame Destination, Inc. In 2004 Mark realized the framing industry was not keeping up with the evolution of photography via new digital technology and started Frame Destination in his garage. Now his company has thousands of do-it-yourself framing customers across the US that it helps with its 11,000 square feet production facility in Dallas, TX.

2 thoughts on “Proper Mat Size for Matting an Image”

  • Trotter Hardy

    Hi. Just noticed something. Above, you say this: "All mats from our shop feature smaller windows than most store-bought mats, meaning more of the image showing through in a framed piece."
    I think you mean either "smaller BORDERS" or "LARGER windows," not "smaller windows." Otherwise, a very helpful explanation--thanks.

  • Mark Rogers

    Thanks Trotter, you are correct the window is larger not smaller. Great catch!


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