Matting
Mat Opening Calculator
The mat opening (window) is cut a little smaller than your artwork so the mat can hold it. Enter the artwork and overlap to get the exact opening size — or switch to reverse to find the overlap from an opening you already have, in inches or centimeters.
Standard range ⅛–¼″ — enough lip to hold the art without hiding it.
- Mat opening (window)
- 7 1/2″ × 9 1/2″ 19.1 × 24.1 cm
- Cut smaller per side
- 1/4″ 0.6 cm
How the mat opening calculator works
The mat opening — the window — is the hole your artwork shows through, and it’s cut a little smaller than the art so the mat can hold it. Enter your artwork size and an overlap, and this tool gives you the exact window to cut, in inches with fractions or in centimeters.
Which tool?
Use this calculator when you know the opening (or the overlap) and need the window cut. If you instead know the border width you want and need the outside and frame size, the mat border calculator is the one to reach for.
The math is simple: opening = artwork − 2 × overlap in each direction. The overlap is the small lip of mat board that sits over the edge of the print so it can’t slip out the front. A ¼″ overlap is standard, so an 8 × 10″ print needs a 7½ × 9½″ window — a ½″ smaller in each dimension because the ¼″ is taken off both sides.
The opening is only part of the picture. Once you know the window, the mat border calculator adds your borders to get the mat’s outside size — which is the frame you order — and the multi-opening mat calculator repeats the window across a grid for a collage.
Switch the tool to reverse mode when you already have an opening and want the overlap. Enter the artwork and the existing window and it returns the overlap on each side: overlap = (artwork − opening) ÷ 2 per dimension. That’s the quick way to match an old mat, copy a frame you liked, or sanity-check a custom-cut order before you pay for it. UK and Australian framers call the opening an aperture, but the measurement is identical.
Choosing the overlap
The overlap is a trade-off between hold and visible image. A ¼″ lip is plenty for ordinary prints and photos, and it’s what most pre-cut mats use. Drop to ⅛″ when the art runs close to its edge — a print with a thin white margin, a stamp, a small original — so the mat doesn’t bite into the picture. Go wider than ¼″ only for heavy or curling paper that needs more grip. Whatever you pick, keep it equal on all four sides unless you’re deliberately shifting the image off-center.
Measure the artwork itself, not the paper it’s printed on, if you want the image centered in the window. For a print with an uneven white border, decide up front whether you’re matting to the image or to the sheet, and measure to that edge — mixing the two is the usual reason a finished window ends up looking slightly crooked. If the art isn’t a tidy rectangle, measure its widest and tallest points and let a little extra overlap hide the irregular edge.
Reverse mode: find the overlap from an opening
Already have a pre-cut mat, or a window you measured from a frame you liked? Flip the tool to reverse mode, enter the artwork and the existing opening, and it returns the overlap each side is giving you: overlap = (artwork − opening) ÷ 2 per dimension. A 7½ × 9½″ window holding an 8 × 10″ print, for instance, works out to a ¼″ overlap all around.
It’s the quickest way to judge a store-bought mat before you trust it to your art. If the implied overlap comes back under ⅛″, the mat barely grips and the print can creep forward; if it’s well over ¼″, the mat is eating into the image. Reverse mode also catches a mislabeled custom-cut order — punch in what you asked for against what arrived, and any mismatch shows up as an overlap that isn’t the ¼″ you expected.
Worked example: an 8×10 print at ¼″ overlap
Start with an 8 × 10″ print and the standard ¼″ overlap. Take ¼″ off each side: 8 − ¼ − ¼ = 7½″ wide, and 10 − ¼ − ¼ = 9½″ tall. So you cut a 7½ × 9½″ window. Run it backwards to check: an 8 × 10″ print in a 7½ × 9½″ window means (8 − 7½) ÷ 2 = ¼″ of overlap on the left and right, and the same top and bottom — exactly what you set.
Common mistakes
- Cutting the window to the print size. An 8 × 10 window for an 8 × 10 print leaves nothing to hold the photo — it drops straight through. Always subtract the overlap.
- Counting the overlap once. The ¼″ comes off both sides, so the window is ½″ smaller per dimension, not ¼″.
- Too much overlap on small art. A ¼″ lip can swallow a 4×6 snapshot’s border; drop to ⅛″ to keep more of the image visible.
- Confusing the opening with the border. The opening is the window in the middle; the border is the mat around it. Size the border with the mat border calculator.
Frequently asked questions
How much smaller should the mat opening be than the photo?
About ½ inch smaller overall — ¼ inch on each side. That ¼-inch lip is the overlap that holds the print, so an 8×10 photo gets a 7½ × 9½ inch window. For very small or delicate art you can drop to ⅛ inch per side to show more of the image.
What is the mat opening (window)?
The opening, or window, is the hole cut in the mat that your artwork shows through. It is cut a little smaller than the art so the beveled edge of the mat overlaps and grips the print. UK and Australian framers call it the aperture.
How much should the mat overlap the artwork?
¼ inch on each side is the standard overlap — enough to hold the print securely without covering much of the image. Thin or full-bleed art can use ⅛ inch. Whatever you choose, the window equals the artwork minus twice that overlap.
Can I work out the overlap from an opening I already have?
Yes — switch the tool to reverse mode. Enter the artwork size and the existing opening and it returns the overlap on each side, which is handy for matching an old mat or checking a custom-cut order before you pay for it.
Should the opening be the same size as the print?
No. If the window matched the print exactly, the mat would have nothing to hold and the art would fall through. The opening is always cut smaller than the artwork by the overlap — typically ¼ inch per side.