How to measure artwork for matting

The short answer

To measure for a mat, measure the artwork's width and height at the image edges to the nearest 1/16 inch, then make the mat opening (the window, or aperture) a quarter inch smaller on every side so the mat overlaps the art and it can't slip through.

In one line: opening = artwork − 2 × overlap, with a default overlap of a quarter inch per side. Everything below is just that idea, slowed down so nothing gets cut wrong.

Measure for a mat, step by step

1. Measure the image, not the paper. Lay the artwork flat and measure the width and height at the image edges to the nearest sixteenth inch (or nearest millimeter). Ignore the paper margin and any backing board.
2. Decide the overlap. Pick how much mat will cover the edge of the art. A quarter inch per side is typical; drop to an eighth inch for tiny or full-bleed prints.
3. Subtract twice the overlap. The window is smaller on both sides, so opening = artwork minus two times the overlap on each dimension. At a quarter-inch overlap that is the art minus half an inch.
4. Mark the opening centered on the board. Center the opening on the mat board (or hand the numbers to your cutter or the calculator) and mark it lightly on the back before any blade touches the board.
5. Measure twice, cut once. Re-measure the art and your marks before cutting. A second check catches a swapped width and height or a slipped tape, which is far cheaper than a ruined sheet of board.

How it works

A mat (UK: a mount, cut from mount board) is a board with a window cut in it. The window has to be a touch smaller than the art so a thin lip of board rests on the edge and holds the print in place. That lip is the overlap.

Because the window shrinks on the left and the right, you subtract the overlap twice across the width — and likewise twice down the height. That is the whole formula:

• opening width = art width − (2 × overlap)
• opening height = art height − (2 × overlap)

The default overlap is a quarter inch (0.25″) per side, which subtracts half an inch from each overall dimension. The sensible range is an eighth to a quarter inch: smaller for tiny or full-bleed art, larger when you want a confident, secure grip. Centimeter worker? Use 6 mm per side as your quarter-inch equivalent and work to the nearest millimeter.

Why subtract on both sides rather than just trim a hair off one edge? Because the window is a hole in the middle of the board. Shrink only the right edge and the art slides left until it pokes out the top; the lip has to surround the art for the print to stay put. Picture the opening as a rectangle floating inside the artwork outline — the overlap is the even margin between the two, and there are four of those margins to account for.

Choosing your overlap

A quarter inch is the safe default for almost everything from snapshots to posters. It's generous enough to hide the occasional ragged edge or a thin white border you'd rather not see, and it leaves a comfortable lip even if your cutting drifts a sixteenth.

Reach for an eighth inch when the art is small — a 4 × 6″ print loses a noticeable chunk of itself to a quarter-inch lip on each side — or when the image runs full-bleed to the paper's edge and every millimeter of it matters. Below an eighth inch, a hand-cut bevel gets fragile and the art can work loose, so treat that as the floor unless you're hinging the piece some other way.

Worked example: an 8 × 10″ print

Say you have a standard 8 × 10″ print and you want the usual quarter-inch overlap. Subtract half an inch (two quarters) from each dimension:

1. Width: 8 − (2 × 0.25) = 8 − 0.5 = 7½″
2. Height: 10 − (2 × 0.25) = 10 − 0.5 = 9½″

So the opening is 7½ × 9½″, centered on the board. Want to skip the arithmetic and account for the board size too? Drop the print dimensions into the mat opening calculator and now get your exact window size in fractions or millimeters.

Notice what happened to the numbers: each dimension lost half an inch, not a quarter. That half inch is the two quarter-inch lips added together. If you'd wanted an eighth-inch overlap instead, you'd subtract a quarter inch overall and land at 7¾ × 9¾″. Same art, different grip, different window — which is exactly why you decide the overlap before you cut, not after.

What you need to measure well

You don't need a workshop. A rigid steel rule or a tape that reads in sixteenths is plenty; a clear acrylic grid ruler is even nicer because you can line it up on the image edge and read the dimension directly. Lay the art on a flat surface, square the rule to the edge, and read the measurement straight on — not at an angle, which fattens every number. Jot both the width and the height down immediately so you're never holding two figures in your head at the cutter.

Measuring odd cases

Not every piece is a clean rectangle with a printed image inside a tidy paper margin. Before you touch the ruler, decide what the mat should hide and what it should deliberately show. That decision controls the "art size" you put into the formula.

Deckled or torn edges

If the ragged paper edge is part of the piece, do not measure only the inked image. Measure the full edge you want visible and plan a mat opening that shows it cleanly. If the deckle is just rough paper you want covered, measure the image area inside it and let the overlap hide the uneven outside.

Signatures, edition numbers and titles

A pencil signature, title or edition number below a print is usually meant to stay visible. In that case, measure from the left image edge to the right image edge, then measure the height down to include the signature line. If the writing is not part of the finished presentation, measure the image only and treat the extra paper as margin.

Artwork that is not square

Handmade paper, fabric-backed work and trimmed prints can be wider at one end than the other. Measure width at both the top and bottom, height at both left and right, then use the smaller measurement for the opening math. The mat lip will still cover the larger side; using the larger measurement risks exposing a sliver of uneven edge.

Working from a pre-cut mat instead of raw art? Use the mat opening calculator in reverse: enter the artwork and the existing opening to see the implied overlap on each side. If the overlap comes back uneven, you know the mat is doing some of the hiding for you.

Quick reference: common prints

Matting a standard photo size at the usual quarter-inch overlap? Every opening is simply the print minus half an inch on each dimension. Here are the sizes you'll meet most often.

Common mistakes

• Measuring the paper or backing instead of the image. The mat covers a sliver of the image edge, so always measure the picture you want to show — not the white margin around it.
• Making the opening the same size as the art. A window the size of the print has nothing to grip, so the art drops straight through. The opening must be smaller.
• Subtracting the overlap only once. The window shrinks on both sides of each dimension, so subtract 2 × overlap per dimension — not a single quarter inch off the total.
• Mixing decimals and sixteenths. Pick one notation and stick to it. Rounding 7.4375″ in your head as "about 7½" twice over is how an opening drifts an eighth of an inch off.
• Assuming the art is perfectly rectangular. Hand-torn or trimmed prints rarely are. Measure both opposite edges, and if they differ, use the smaller one so the mat covers the wider side too.

Working in metric? The same rules apply — just measure to the nearest millimeter and subtract 6 mm per side. Don't half-convert: an opening that's "12 cm-ish" is exactly the kind of fuzzy number that bites you at the cutter.

Why "measure twice" earns its cliché

The single most common ruined mat comes from swapping width and height — marking a 9½ × 7½″ window for a portrait print, or cutting to the frame's orientation instead of the art's. A board is cheap, but it isn't free, and a wrong cut can't be uncut. Re-measuring the art and re-reading your pencil marks takes ten seconds and saves the sheet.

A good habit: write the opening size on a sticky note and physically hold it against the art before you commit the blade. If the note says 7½ × 9½″ and the print clearly looks taller than it is wide, the numbers and the picture agree and you're clear to cut.

After you've measured

Measuring the art settles the inside of the mat. The other half of the job is the border — how much board shows around the opening — which sets the finished frame size. That's a separate decision, and our guide to how wide a mat border should be walks through the proportions and the classic bottom-weighting trick.

Once you know both the opening and the border you want, the mat border calculator turns them into a full cut list. And if you're placing several pictures under one mat, the openings interact, so follow the multi-opening mat guide rather than treating each window in isolation.

Terms worth knowing

Overlap (lip)

The strip of mat that rests on the edge of the art and holds it. A quarter inch is standard; an eighth inch for small work.

Opening / aperture / window

The hole cut in the mat that the art shows through — always smaller than the art by twice the overlap.

Mount board

The UK and Australian term for mat board — the same product, a stiff faced board you cut the window from.