Matting
Mat Border Calculator
Enter your artwork size and border width to get the exact mat opening and outside (frame) dimensions — in inches or centimeters.
Standard range ⅛–¼″ — enough lip to hold the art without hiding it.
- Mat opening
- 7 1/2″ × 9 1/2″ 19.1 × 24.1 cm
- Mat outside
- 11 1/2″ × 13 1/2″ 29.2 × 34.3 cm
- Borders (T / B / L / R)
- 2″ / 2″ / 2″ / 2″ 5.1 cm / 5.1 cm / 5.1 cm / 5.1 cm
How the mat border calculator works
A mat does two jobs: it holds your artwork in place and gives the image room to breathe inside the frame. This calculator turns an artwork size and a border width into the two numbers you actually need — the opening (the window the mat is cut to) and the outside (the size of the frame you order).
Which tool?
Use this calculator when you know the border width you want and need the sizes it produces. If instead you already know the window — or want the overlap from a pre-cut mat — the mat opening calculator is the one to reach for.
The window is your artwork minus the overlap on every side — the small lip of mat board that sits over the edge of the print so it can’t slip through. The math is two short steps: opening = artwork − 2 × overlap, then outside = opening + 2 × border, run on each dimension. With a ¼″ overlap, an 8 × 10″ print needs a 7½ × 9½″ window; add a 2″ border and the outside is 11½ × 13½″. Because a frame’s rabbet — the groove the glass and art sit in — matches the mat’s outside, that outside is exactly the frame size you buy.
Equal borders all the way around are the simplest choice, and what the tool shows first. Many framers then add a little to the bottom — bottom-weighting — because the optical center of a frame sits slightly above the true center, so an even mat can make the picture look like it’s sinking. Adding ½–1″ to the bottom border lifts the art back to where the eye expects it; the calculator shows the equal and bottom-weighted numbers side by side so you can decide.
For a layered look, framers sometimes set a second mat behind the first so a thin line of color — the reveal — shows around the window. That’s a double mat; this tool sizes the top mat, and the double matting & reveals guide covers adding the reveal underneath. Everything works in inches with fractions or in centimeters — switch units with the toggle and the values convert in place. In the UK and Australia the mat is a mount and the window an aperture; the measurements don’t change with the name.
Worked example: an 8×10 print with a 2″ border
Take an 8 × 10″ print and a 2″ border. The ¼″ overlap makes the window 7½ × 9½″; adding 2″ on every side makes the outside 11½ × 13½″ — so you’d order an 11½ × 13½″ frame (or round up to a 12 × 16 and widen the borders to suit). The glass and backing drop in about ⅛″ smaller, at roughly 11⅜ × 13⅜″.
Want the print optically centered? Keep 2″ at the sides and top and use 2½″ at the bottom. The window stays 7½ × 9½″, but the outside grows to 11½ × 14″. Check any print-and-frame pairing with will it fit, or size the glass on its own with the glass size calculator.
Choosing a border width
Border width is mostly taste, but scale is a good guide. Small snapshots up to 5×7 look tidy with 1½–2″; the classic 8×10-to-11×14 range sits well at 2–2½″; and large pieces earn their space with 3″ or more. A wider mat almost always looks more deliberate than a narrow one, and it’s the cheapest way to make a modest print feel gallery-framed — when in doubt, go a little wider than feels natural.
One reliable rule of thumb: the mat border should be wider than the frame moulding, so the eye reads mat-then-frame rather than one thick edge. If your frame is 1″ wide, a 2″-plus mat keeps that hierarchy and stops the moulding from crowding the art. Square artwork is the exception worth naming — equal borders on a square can look static, so many framers widen the bottom slightly even there to give it a base.
| Artwork size | Border (each side) | Look |
|---|---|---|
| 4×6 – 5×7 | 1½–2″ | Tidy, snapshot |
| 8×10 – 11×14 | 2–2½″ | Classic |
| 16×20 – 18×24 | 3″ | Gallery |
| 24×36 and up | 3½–4″ | Statement |
Common mistakes
- Cutting the window the same size as the art. The opening must be ¼″ smaller per side, or the mat has nothing to grip and the print slips through.
- Forgetting the border counts twice. A 2″ border adds 4″ to each dimension — 2″ on each side — not 2″. An 8×10 with 2″ borders needs an 11½″-wide frame once the overlap is counted, not a 10″ one.
- Equal borders that look bottom-heavy. If a finished piece seems to sag, you probably want bottom-weighting — the bottom-weighting guide explains why and by how much.
- Mixing inches and centimeters. Pick one unit and let the toggle convert everything, so you’re never adding 2″ to a 30 cm number by hand.
Standard print & mat pairings
Buying a pre-cut mat instead of cutting one? Each common print size pairs with a stock mat (and the frame of the same outer size) that holds it. The full chart with window and border numbers lives on standard mat sizes.
| Print size | Standard mat / frame |
|---|---|
| 4 × 6″ | 5 × 7″ |
| 5 × 7″ | 8 × 10″ |
| 8 × 10″ | 11 × 14″ |
| 11 × 14″ | 16 × 20″ |
| 16 × 20″ | 20 × 24″ |
| 20 × 30″ | 24 × 36″ |
Frequently asked questions
How wide should a mat border be?
A safe default is 2–3 inches on the top and sides for art up to about 16×20, widening to 3–4 inches for larger pieces. Wider mats read as more gallery-like and give the eye room to rest, while a too-narrow border can look like an afterthought. Match the border to the art and the wall rather than to a fixed rule.
Should the bottom border be larger than the top?
Often, yes — it is called bottom-weighting. The visual center of a frame sits a little above the true center, so an equal mat can make the image look like it is sinking. Adding roughly ½ to 1 inch to the bottom border lifts the art to where the eye expects it. The calculator shows both the equal and bottom-weighted numbers so you can compare.
What size mat do I need for an 8×10 photo?
With a 2-inch border, an 8×10 photo gives a 7½ × 9½ inch window and an 11½ × 13½ inch outside — and that outside is the frame size you order. Drop the photo size and border into the calculator to see the window, outside, and glass sizes together, then change the border width to taste.
How do I calculate mat size for a frame?
Work outward from the art. The opening is the artwork minus the overlap (about ¼ inch per side) so the mat can hold the print; the outside is the opening plus your chosen borders, and that outside equals the frame’s rabbet — the size you buy. The calculator runs it in both directions, in inches or centimeters.
How much overlap holds the artwork in place?
About ¼ inch on each side is standard — enough for the mat to grip the print without hiding much of the image. For very small art, ⅛ inch keeps more of the picture visible. That overlap is exactly why the window is cut a little smaller than the artwork.