Understanding Mat Board Window Openings

Written by Mark Rogers

Today, let’s talk about mat board window openings. It may not sound like an exciting topic, but understanding how to calculate mat board window opening sizes is a crucial skill for DIY picture framers.

The mat window opening, also known as the exact mat opening, is the opening that is cut in a mat board through which the image can be viewed.

mat window opening example

Standard mat window openings are cut slightly smaller than the actual image size — this is called “cropping” the image. The opening is smaller in order to cover the edge of the image or any surrounding white border if it is a print. This is both an aesthetic (it looks better) and a practical choice; you don’t want the image to fall through the window opening if it’s cut too large!

Standard, off-the-shelf frames that come with mats usually crop ¼ inch on all four sides. Frame Destination cuts our popular size mat windows 1/8-inch smaller than the image to allow for maximum exposure of your image without a loss of detail. For images that are larger than 18” x 24”, our standard crop is ¼-inch.
Example: Your image measures exactly 8” x 10”. This is the actual image size, exclusive of any white borders, if it is a print. If you choose an 8” x 10” mat in one of our popular sizes, the actual window opening size will be 7 3/4” x 9 3/4”, which crops 1/8-inch of the image on all four sides.

Example: Your image measures exactly 8” x 10”. This is the actual image size, exclusive of any white borders, if it is a print. If you choose an 8” x 10” mat in one of our popular sizes, the actual window opening size will be 7 3/4” x 9 3/4”, which crops 1/8-inch of the image on all four sides.

mat window dimensions

If you prefer less or more cropping of the image, check the “customize this preset frame size” box and select your preferences. You can also always contact us for advice on the best mat window opening size for your artwork.

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15 thoughts on “Understanding Mat Board Window Openings”

  • Carolyn

    I have a poster (10 actually) that is printed full bleed on 11 x 17 stock, i only want about 1/4 to 1/2 inch cover by the mat and I will put it in a barnwood frame. Do I need a mat opening of 10.5 by 16.5?
    and if the mat is 1 inch wide - wht is the opening of the frame. i know the width of the frame runners could be 1 to several inches but what is the opening? the poster is the banner on my website - the village of our carvings.

    • Mark Rogers

      If you make the mat opening 10.5 x 16.5 then the mat will cover up 1/4 inch on all 4 sides. This makes it easy to get placed in the mat but if you want more of the poster to show you can 10.75 x 16.75. Most frames overlap the mat by about 3/16 inch. 1" is kind of small. I would go at least 1-1/2 inch which results in the outer mat size and frame size of 13-3/4 x 19-3/4 if you go for the 10.75x16.75 opening.
      We have more info about frame dimensions here:
      Info about custom mats here:

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  • Toi

    I have a 10x15 single weight mat board print (50 pt depth), what size frame should I get?

  • Mark Rogers

    Toi, if 10x15 is the outside of the mat and not the window size then you would order a 10x15 frame.

  • Catherine Patterson
    Catherine Patterson March 10, 2017 at 6:29 am

    I have a 16" x 36" poster. What size matte do I need?

  • Mark Rogers

    Catherine, It is typical to have the mat window overlap the print by 1/4 inch. If you use artwork overlap of 1/4 inch the mat opening will be 15-1/2 x 36-1/2. I would use 2 or 3 inch mat borders which results in an external mat size (also the picture frame size) of 19-1/2 x 39-1/2 or 21-1/2 x 41-1/2.

  • lasertest

    It's hard to come by educated people in this particular subject, but you sound like
    you know what you're talking about! Thanks

  • carolyn

    I have a frame sized 19 1/2 x 24 7/8 that I want to put a certificate in. The certificate measures 15 1/2 x 21. What size mat do I need?

  • Mark Rogers

    Our mat pages have a calculator to determine that:
    Just select the mat type you would like, click on "specify mat" with window mat selected.
    Click customize your mat size since you have a custom frame.
    After you enter the size of your certificate, enter the artwork overlap.
    I used 1/8" which means the mat will cover 1/8" on all 4 sides.
    With "outside mat size" selected, enter the frame size.
    Your opening would then be 15-1/4" x 20-3/4" with Side borders of 2-1/8" and the top and bottom would be 2-1/16".

    When you say the frame size is 19-1/2 x 24-7/8 that should be the inside of the frame, or the size of the glass that would fit in the frame. The outside dim of the mat will equal the glass size.

  • Jennifer gillespie
    Jennifer gillespie December 7, 2017 at 2:12 pm

    I have broadway play bills that measure 5 and 3/4 inches by 8 and 7/8 inches. Can you tell me what size standard frame I would get?

    • Mark Rogers

      Hi Jennifer, I would use a mat window of 5 1/2" x 8 5/8". If you use side borders of 2-3/4 and top and bottom borders of 2-11/16 it will fit in a standard 11x14 picture frame.

  • Daija Saulsberry
    Daija Saulsberry January 8, 2018 at 5:45 am

    I have artwork that is on an 18x18 inch sheet; however, the drawing that is on the sheet is 17x17 inches. What size should the opening of my 18x18 inch mat board be? I was thinking 17 1/4 so that most of my drawing is seen. What do you think?

    • Mark Rogers

      Hi Daija,

      Typically if you are going to show some paper border around the drawing the border is at least 1/4 inch which means the opening should be 1/2 inch larger or 17-1/2 x 17-1/2 inches.

  • Sara

    Hi Mark
    I would like to know why is it necessary to use an overlap of 1/4 all around for pictures bigger that 18x24?
    I work in a framing department myself and I have noticed that using 1/8 overlap for big mats is usually not enough. The picture ended up falling out the mat... Why is that?
    I am very curious about this mystery

    • Mark Rogers

      Sara, I think it is because if the paper curls a little it will not be as large combined with the larger paper being heavier and needing a little more support to stay flat. I suspect if it is dry mounted it is less of an issue, but still it can be harder to get those larger images perfectly centered in the mat when framing.

  • Linda Dixon

    What would the opening be for a 20x30 picture on a 24x36 mat board?

  • Janice Kramer
    Janice Kramer July 28, 2019 at 1:23 pm

    I want an 11 x 14 black frame, matted for a 5 x 7 print but I want this opening toward the top of the frame/matting. What am I asking for so I can search for this?

  • Barb Marshall

    I have a print to frame that is 18” x 24”. I want a very thin mat. Would you suggest the 1/4”? Do I need to special order the frame?

    • Heather

      Hi Barb! We carry 4ply and 8 ply mats, 4ply mats are 1/16" thick and 8ply mats are 1/8" thick. The depth would depend on your preference and the frame you chose.

      Thanks and have a great day!

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