Mat Board Calculator in Inches or Centimetres
A mat board calculator for one job: an 8 × 10 in picture in a 16 × 20 in frame, with the opening and every border in inches and a cutting diagram to cut from.
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- Frame size
- Mat opening
- Side borders
- Top border
- Bottom border
How to cut a mat board opening
The page opens on the example above, so the numbers in the first row of the table are the first thing you see.
- Choose inches. Type the frame size as the window the mat board has to fill, measured inside the frame. The outside edge of the frame is wider, so do not use it.
- Type the picture size as printed and the overlap, the width the mat covers on each side. The example uses a quarter inch, 0.25 in.
- Read the opening. It is the picture minus twice the overlap, so an 8 × 10 in picture gives a 7.50 × 9.50 in opening.
- Read the three borders. Each side border is 4.25 in and the top and bottom borders are 5.25 in each for this frame.
- Press Print the cutting diagram and mark the opening from the numbers on it. Measure twice against the numbers, not the drawing, because the drawing is scaled to the page.
Why the example is in inches
The example is in inches because the frame, the picture and the mat board in it are all measured that way. In centimetres the same 16 × 20 in frame is 40.64 × 50.8 cm, and the calculator gives the same borders in either unit.
The overlap is easy to leave out. It has its own box on the page, because a mat cut to the picture's exact size lets the picture drop through the opening.
Four mat board cuts in inches
| Frame | Picture | Overlap | Opening | Side borders | Top and bottom borders |
|---|---|---|---|---|---|
| 16 × 20 in | 8 × 10 in | 0.25 in | 7.50 × 9.50 in | 4.25 in | 5.25 and 5.25 in |
| 16 × 20 in, weighted bottom | 8 × 10 in | 0.25 in | 7.50 × 9.50 in | 4.25 in | 4.20 and 6.30 in |
| 11 × 14 in | 8 × 10 in | 0.25 in | 7.50 × 9.50 in | 1.75 in | 2.25 and 2.25 in |
| 8 × 10 in | 5 × 7 in | 0.25 in | 4.50 × 6.50 in | 1.75 in | 1.75 and 1.75 in |
The opening is smaller than the picture
The opening is the picture minus twice the overlap in each direction. An 8 × 10 in picture with a 0.25 in overlap gives a 7.50 × 9.50 in opening. The picture sits behind the board, and the board covers a quarter inch of it on every side.
The same rule holds for any size. A 5 × 7 in picture in the same kind of board has a 4.50 × 6.50 in opening, and that is the last row of the table.
The borders come from the space left over
The side border is the frame width minus the opening width, divided by two. For a 16 in wide frame and a 7.50 in opening that is 4.25 in on each side. The top and bottom share the 20 in height minus the 9.50 in opening, which is 10.50 in, so each border is 5.25 in when the bottom is not weighted.
With the bottom weighted, the 10.50 in is split 40 and 60. The top becomes 4.20 in and the bottom 6.30 in. Both add up to the same 10.50 in, so the board does not change size.
Inches and centimetres give the same cut
Each inch is 2.54 cm, so a 16 × 20 in frame is 40.64 × 50.8 cm and an 8 × 10 in picture is 20.32 × 25.4 cm. The opening of 7.50 × 9.50 in is 19.05 × 24.13 cm, and the borders convert the same way.
The calculator works in centimetres inside and converts once when you type, so switching the unit changes the numbers you see and not the cut.
Tips for better results
- Check the opening against a steel rule before you cut, using the numbers from the cutting diagram rather than the drawing.
- Measure the window the board has to fill, not the outside of the frame. The outside is always wider.
- Type in inches for a frame bought in inches. Switching units converts the numbers already in the boxes.
- If the calculator says a border is narrower than the overlap, the picture would show past the board. Widen the border or reduce the overlap.
- Trust the printed numbers over the drawing. The drawing is scaled to fit the page, and the numbers are the measurements.
Privacy
Your photo, if you add one for the preview, never leaves your device. The numbers are worked out in your browser, and nothing is uploaded or stored.
Frequently asked questions
How do I work out the opening of a mat board?
Take twice the overlap off each side of the picture size. For an 8 × 10 in picture with a 0.25 in overlap, the opening is 7.50 × 9.50 in, because a quarter inch is taken off each side of each dimension. The calculator does this sum for you as you type.
What border should a mat board have?
The border is your choice, and the calculator works both ways. Type the frame to read the borders, or type the picture and the border you want to read the frame size. A 16 × 20 in frame around an 8 × 10 in picture gives 4.25 in on each side.
Can I use the mat board calculator in inches?
Yes. Choose inches and type the sizes in inches. The 16 × 20 in example gives the same borders as 40.64 × 50.8 cm, because the calculator converts each typed size once and shows the results in the unit you chose.
Why does a mat board need an overlap?
The overlap keeps the picture behind the mat. Without it the opening would be the same size as the picture, and the picture could slip through. A quarter inch covers the edge of an 8 × 10 in picture by that much on every side.
Does a weighted bottom change the size of the board?
No. The weighting only moves the opening up. For the 16 × 20 in frame the top border becomes 4.20 in and the bottom 6.30 in, which together still make the 10.50 in of vertical border the board has to give.
Related tools and guides
- Picture Mat Calculator: Opening, Borders and Cutting Diagram: Work out the mat opening and borders for a frame and picture, or the frame size from a picture and a border.
- Photo Mat Size: Find the Frame From Your Picture: Type the size of your picture and the border you want on the sides and top, and read the frame size a photo mat needs. The example is a 20 × 30 cm picture in a 30 × 40 cm frame.
- Gallery Wall Planner: frames at real sizes: Lay out a gallery wall with ready grids or your own frame sizes, then read the measurements to hang it.
- Work out how large your photo can print: Convert pixels and print dimensions; change JPEG DPI tags.
- Print a Poster on Multiple Pages: Split a large image into paper sheets for a poster, with overlap and a printable PDF.
- Make a contact sheet of your photos: Print a page of thumbnails with captions and EXIF lines as a PDF or page images.
- I Built the Tools I Kept Looking For as a Photographer: Why these calculators run in your browser instead of on a server.