How to Size a Picture Frame Mat

Peter Macdiarmid/Getty Images News/Getty Images

A mat enhances a finished work of art or photograph helping to frame the work. You can choose from a standard white or black mat or branch out into a variety of colors pulling from the art work to match or complement the décor of a room. A double or triple mat adds extra flair to the presentation of the piece. You can purchase mat board in multiple colors at some arts and craft stores, most art supply stores and online.

Choose a piece of art or photography to be matted. Choose a frame type. The frame size will be determined based on the calculations of the finished matted art. Choose the color or colors of mat that match or complement the art work and the frame. Most stores where you can purchase mat board also have sample corners that allow you to “see” what the mat colors will look like with the art.

To calculate the mat, use the inner measurement of the frame for the outer measurement of the mat. The inner cut of the mat will be at least 1/4th inch inside the outer dimension of the art work. It is best to cut the mat proportional to the frame. Most mats are at least 2 inches wide and not more than 4 inches wide.

If you have an 8-inch by 10-inch photo and you want a mat that is approximately 4 inches wide, you will want a 12- by 14-inch frame. Remember that you need the inner cut of the mat to be 1/4 of an inch smaller than the photo. Calculate 7 3/4 + 4 1/4 = 12 and 9 3/4 + 4 1/4 = 14. That makes the outer mat 12 by 14 and the inner cut 7 3/4 by 9 3/4, making the mat 4 1/4 inches. Some frame stores may carry a 12- by 14-inch frame, however this mat makes the frame custom.

To figure the mat starting from a standard frame size, make the outer mat the size of the frame. For example, a 16- by 20-inch frame would need an outer mat that is 16 by 20. If you want a 4-inch mat, the art work needs to be 8 1/4 x 12 1/4. You may have to play with the numbers to get an agreeable proportion between the available frames and your art work.

Add an extra 1/4 inch to the width of the mat frame to deal with an optical illusion that happens, especially to very large works of art. The extra 1/4 inch is not noticeable, but it helps weigh the art work down, because it pulls the eye down, but still looks like the mat is the same dimension all around. This is a trick artists and galleries use when preparing art for display.

Things You'll Need

  • Art work or photograph
  • Mat board
  • Yard stick or ruler
  • Pencil
  • White eraser


  • You can use these rules to figure out the size of pre-cut mats from a store. There is a very limited range of sizes.