One wrong frame size turns a finished print into a return label. The measurement that decides everything is the mat opening — the window the artwork shows through — not the outer frame size printed on the box, and the two are never the same number. Get that distinction straight and an 18×24 print frames correctly every time, whether you want it edge-to-edge or matted in a wider border.
What Frame Size Fits An 18×24 Print?
An 18×24 print drops straight into an 18×24 frame when you skip the mat. That is the direct sizing rule: artwork dimensions match frame dimensions, and the print runs edge to edge behind the glazing.
There is one catch worth knowing before you buy. Framing guides note that the visible display area in an unmatted 18×24 frame can land around 17.5×23.5, because the frame’s rabbet — the inner lip that holds the glass and backing — overlaps the outer edge of the print. So an unmatted 18×24 is not delivering a full 18×24 of visible image. The lip typically covers the border area, which is fine for prints with white margins and a problem for artwork with detail running to the very edge.
How Much Larger Should A Frame Be With A Mat?
Add a mat and the outer frame grows while the opening stays slightly smaller than the art.
Two different mat openings show up across framing sources for the same 18×24 print:
The overlap is the point. A mat opening cut slightly smaller than the artwork creates a lip that holds the print flat against the backing, so it cannot slip down inside the frame. Cut the opening to match the artwork exactly and there is nothing holding it — the print shifts, and eventually it falls behind the mat.
Border width works out from there. If you would rather buy a frame that already has the matting worked out for you, this roundup of popular 18 x 24 matted picture frame options compares ready-made choices that match these opening sizes.
| Outer Frame Size | Mat Opening For 18×24 Art | Result |
|---|---|---|
| 18×24 | None | Edge-to-edge; visible area near 17.5×23.5 |
| 22×28 | 17.5×23.5 | About 2.5-3 inch mat border |
| 24×30 | 17.5×23.5 | About 3 inch mat border |
| 18×24 | 11.5×17.5 (for 12×18 art) | Shows mat convention at smaller print sizes |
Why Do Mat Openings Differ Between Frame Shops?
Frame shops do not cut mats to one universal standard.
Custom shops sometimes tighten it for prints where showing more image matters.
The practical test is simple. Measure your actual artwork’s printed area — not the paper, the image — and confirm the mat opening overlaps it by an eighth to a quarter inch per side. Do not order a mat opening equal to the artwork size.
Framing Mistakes To Avoid Before You Buy
The most common errors all trace back to mixing up two measurements that sound interchangeable but are not.
- Confusing outer frame size with mat opening size. A 24×30 frame does not mean a 24×30 opening; for an 18×24 print, the opening is 17.5×23.5.
- Ordering a mat opening equal to the artwork. Without overlap, nothing secures the print.
- Assuming every shop cuts the same undercut. Ask for the exact opening dimensions in writing before ordering.
- Overlapping too much. Enough mat to hold the print is the standard; too much hides edges that matter.
Larger pieces follow different rules, so the numbers here apply to 18×24 and below. For the exact opening figures, the mat opening dimensions guide lists the standard cuts by print size.
FAQs
Can I put a mat inside an 18×24 frame?
Only if your artwork is smaller than 18×24. A mat for an 18×24 print needs an 18×24 or larger outer frame, since the mat opening is cut smaller than the art.
Is the mat opening always smaller than the artwork?
Cutting the opening to match the artwork exactly removes that hold and risks the print falling behind the mat.
Do all frame shops cut mats the same way?
Confirm the exact opening dimensions before ordering a custom mat.
References & Sources
- Frame Destination. “Mat Openings.” Lists standard mat opening dimensions by print size, including the quarter-inch undercut.
- Matboard Center. “How to Choose Your Mat Board Size.” Explains mat border sizing and the frame-size math for standard print dimensions.
- Patchogue Arts Council. “Matting and Framing Presentation.” Covers framing conventions including mat opening cuts and overlaps.
