Picture Mat Calculator: Opening, Borders and Cutting Diagram
Enter a frame and a picture in cm or inches and read the mat opening, the borders and a cutting diagram. The overlap keeps the picture from falling through.
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- Frame size
- Mat opening
- Side borders
- Top border
- Bottom border
How to calculate a picture mat
- Choose cm or inches. Type the frame size as the window the mat has to fill, which is the inside of the frame, not its outer edge. The common frame sizes are one press away.
- Type the picture size and the overlap, the width the mat covers on each side. The calculator starts at 0.5 cm.
- Read the mat size, the opening and the side, top and bottom borders. They are in the unit you chose and change as soon as you type.
- Tick Weight the bottom if you want the picture to sit a little higher. The bottom border then becomes one and a half times the top, and the total does not change.
- Check the preview at scale, add your photo if you like, then press Print the cutting diagram for the numbers to cut to.
The numbers the calculator starts with
The calculator starts with a 20 × 30 cm picture, a 0.5 cm overlap and a 40 × 50 cm frame. Those are the numbers in the first row of the table below.
The overlap is easy to leave out. A mat cut to the picture's exact size lets the picture drop through, so the opening is made smaller than the picture by one overlap on each side.
Four mats worked out by hand
| Frame | Picture | Overlap | Opening | Side borders | Top and bottom borders |
|---|---|---|---|---|---|
| 40 × 50 cm | 20 × 30 cm | 0.5 cm | 19.0 × 29.0 cm | 10.5 cm | 10.5 and 10.5 cm |
| 40 × 50 cm, weighted bottom | 20 × 30 cm | 0.5 cm | 19.0 × 29.0 cm | 10.5 cm | 8.4 and 12.6 cm |
| 30 × 40 cm | 20 × 30 cm | 0.5 cm | 19.0 × 29.0 cm | 5.5 cm | 5.5 and 5.5 cm |
| 50 × 70 cm | 40 × 50 cm | 1.0 cm | 38.0 × 48.0 cm | 6.0 cm | 11.0 and 11.0 cm |
Why the overlap is the margin of the opening
The opening is the picture minus twice the overlap in each direction. A 20 × 30 cm picture with 0.5 cm overlap gives a 19 × 29 cm opening, so 0.5 cm of the picture is hidden on every side and the picture stays behind the mat.
With the bottom weighted, a top or bottom border narrower than the overlap would let the picture show outside the frame. The calculator says so instead of drawing it.
How the weighted bottom is split
The vertical space left over is the frame height minus the opening height. Without weighting each border gets half of it. With weighting the top gets two parts in five and the bottom three, so the bottom border is one and a half times the top.
For the 40 × 50 cm frame the vertical space is 21 cm. The top border becomes 8.4 cm and the bottom 12.6 cm. Together they still make 21 cm, so the frame size does not change and the opening moves up.
Working back from the picture
Reverse mode starts from the picture and the border you want on the sides and top. The opening is the picture minus twice the overlap, and the frame is the opening plus two borders. A 20 × 30 cm picture with 0.5 cm overlap and a 10.5 cm border needs a 40 × 50 cm frame.
With the bottom weighted, the wanted border is the top one, the bottom is one and a half times it, and the frame is taller by two and a half times the wanted border.
Tips for better results
- Measure the window the mat has to fill, not the outside of the frame. The outside edge is wider than that.
- Type in inches and every result follows the unit. Switching units converts what you typed, so the size of the picture stays the same.
- Try the reverse mode before you buy a frame: type the picture and the border you like and see which frame size it needs.
- Keep the overlap at 0.5 cm, about 0.2 in, unless the picture is very small. A larger overlap hides more of the photograph.
- If the calculator says the picture would stick out, make the frame larger or turn off the weighted bottom.
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
What is the overlap on a picture mat?
The overlap is how far the mat covers the picture on each side. The calculator makes the opening smaller than the picture by twice the overlap, so with 0.5 cm a 20 × 30 cm picture shows through a 19 × 29 cm opening and cannot fall through.
How wide is the border of a 40 × 50 cm mat?
With a 19 × 29 cm opening in a 40 × 50 cm frame, the side borders are 10.5 cm each, and the top and bottom borders are 10.5 cm each when the bottom is not weighted. The calculator shows all three in the unit you chose.
What does weighting the bottom of a mat do?
It moves the opening up. The bottom border becomes one and a half times the top, so with a 21 cm vertical border the top is 8.4 cm and the bottom 12.6 cm. The frame size stays the same.
Can I work out the frame size from a picture?
Yes. Switch to the reverse mode, type the picture size, the overlap and the border you want on the sides and top, and the calculator gives the frame size. A 20 × 30 cm picture with a 10.5 cm border needs a 40 × 50 cm frame.
Is my photo uploaded when I add it for the preview?
No. The photo is read in your browser and shown only in the preview on this page. Nothing is sent to a server, and no account is needed to use the calculator.
Can I type the sizes in inches?
Yes. Choose inches and the boxes and results follow the unit. Switching units converts the numbers already typed, so 16 × 20 in is the same frame as 40.64 × 50.8 cm and the mat results match.
Related tools and guides
- 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.
- 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.