To mat a 24×36 frame correctly, choose a 24×36 mat board and cut an opening ¼” to ½” smaller than your print, so the mat overlaps the artwork by 1/8″–1/4″ on all sides.
A mat isn’t just decorative — it prevents your print from touching the glass and creates visual breathing room. But the wrong size causes the artwork to slip through or look swallowed by the frame. The key is matching the mat board’s outer dimensions to the frame’s inner rabbet (24×36 inches), then cutting a centered opening that overlaps the print by about ¼”.
The One Rule for Mat Opening Size
Your mat opening must be smaller than your artwork so the mat holds the print in place. Subtract ½” from both the width and height of your print. If your print is exactly 24×36, it won’t fit most standard poster frames, which show only a 23.5″ x 35.5″ visible area — you’ll need a custom mat or a larger frame.
Three Common Mat Openings for a 24×36 Frame
These are the go-to dimensions for the most common print sizes. Always measure your actual print first before cutting:
| Print Size | Mat Opening | Border Width |
|---|---|---|
| 20″ x 30″ | 19.5″ x 29.5″ | 2.25″ all sides |
| 18″ x 24″ | 17.5″ x 23.5″ | 3.25″ side / 6.25″ top-bottom |
| 20″ x 32″ | 19.5″ x 31.5″ | 2.25″ side / 1.25″ top-bottom |
| Custom 3″ border | 18″ x 28″ | 3″ all sides |
How to Calculate Your Own Mat Dimensions
If your print isn’t standard, do the math yourself. Start with your frame’s inner opening: for a 24×36 frame, the board outer size is 24×36. Decide your border width (at least 2″, and always wider than the frame’s profile, which is about 1.25″ on a large frame). Then subtract twice the border from the frame dimensions to find your opening.
That extra half inch stops the print from slipping through.
Cutting and Assembly Tips That Save Money
You can cut your own mat with an X-Acto knife and a T-square. Mark the opening on the back of the mat board, then cut ¼” inside your drawn line so the print sits comfortably behind. Use a fresh blade for clean edges. For preservation: pick acid-free, alpha-cellulose mat board, and keep the artwork at least 1 inch from the glass using 1/4″ spacers. If your 24×36 frame came with a thin cardboard backing, replace it with foam core for extra rigidity.
For the simplest route, a pre-made 24×36 frame with mat saves the measuring and cutting entirely while still giving that professional look. Frame Destination’s guide confirms that most standard poster frames are designed for 20×30 prints with a mat, not bare 24×36 prints.
FAQs
Will a 24×36 print fit inside a 24×36 frame without a mat?
Usually not. Most 24×36 poster frames have a visible area of only 23.5″ x 35.5″, so a true 24×36 print will be cropped by about ¼” on each edge. A mat or a custom frame is required for a perfect fit.
What happens if my mat opening is exactly the same size as my print?
The print can slip through the opening or buckle over time. Always cut the opening ¼” to ½” smaller so the mat overlaps and holds the artwork in place by at least 1/8″ per side.
How thick should a mat board be for a large poster frame?
Standard 4-ply mat board is the correct thickness for a 24×36 frame. It provides enough rigidity without making the profile look bulky. For valuable art, use a second layer as a spacer behind the mat to keep the print away from the glass.
References & Sources
- Frame Destination. “Guide to Frame and Mat Dimensions for Common Print Sizes.” Provides standard opening calculations and frame compatibility charts.