How to Measure for a 27 x 20 Picture Frame: Getting the Right Size Print and Mat

For a 27 x 20 frame, measure the inside rabbet, then size the mat opening about 1/8 to 1/4 inch smaller than the artwork on each side.

A tape measure run across the front of the frame tells you almost nothing useful. The number that matters hides on the back, where the glass, mat, and backing actually sit. Get that one measurement right and every other decision — mat opening, border width, print size — falls into place.

Where To Measure A 27 x 20 Frame

Slide the tape across the back of the frame, inside the rabbet — the recessed lip that holds the glass and backing. That inside opening, not the outside molding, is your true frame size.

The rabbet runs slightly larger than the stack it holds, per Logan Graphic’s framing guide, because glass, mat board, and backing all consume depth. If you measured the outer edge instead, you’d order a mat that’s too big and a print that never lines up.

Two numbers to write down:

• Inside opening — the width and height from rabbet to rabbet. This is what your mat’s outer edge must match.
• Rabbet depth — how much room sits between the frame lip and the backing. A thick mat plus foam core can eat this fast.

Worth knowing up front: 27 x 20 is not a standard US print size. A 20 x 24 frame commonly pairs with a 16 x 20 print and a mat opening near 15.5 x 19.5, per Logan’s sizing guide. Treat 27 x 20 as a custom dimension and confirm your actual image area before cutting anything.

How To Size The Mat Opening And Borders

Set the mat opening first, then build the borders out from it. The opening should overlap the artwork by at least 1/8 inch on every side, so the paper edges never peek through and the print can’t slip through the hole.

MatBoardPlus notes that many framers use 1/4 inch per side as the working default. Either figure works; 1/4 inch simply gives more forgiveness if your cut drifts.

From there, the math is plain addition:

1. Start with the artwork’s width and height.
2. Subtract the overlap from each side to get the mat opening. A 16-inch-wide print with 1/4-inch overlap becomes a 15.5-inch opening.
3. Pick your border width. Small to medium art usually looks right with 2–3 inch borders; larger pieces often carry 3–4 inches or more, per Logan’s mat guide.
4. Add left plus right border to the opening width, and top plus bottom to the opening height.
5. Check that result against your measured inside rabbet. They should match within a hair.

The overlap protects the artwork; the border is pure design choice.

Common Measuring Mistakes That Ruin The Fit

The single most expensive error is measuring the frame’s outside molding instead of the inside rabbet.

Other traps that show up again and again:

• Cutting the mat opening to match the print size exactly, which leaves paper edges exposed and lets the print drop through.
• Matching the mat’s outer size to the artwork rather than to the frame opening.
• Ignoring glass and backing thickness when buying a ready-made frame — the stack simply won’t seat.
• Guessing at print dimensions without confirming the actual image area. A “16 x 20 print” with wide white margins has a much smaller visible image.

If you’d rather skip the guesswork entirely, our tested picks for a 27 x 20 picture frame list the options that ship with accurate opening specs.

Is 27 x 20 A Standard Print Size?

No. The framing guides reviewed here describe no official 27 x 20 US print standard — it reads as a custom frame dimension. That means the print inside it is almost certainly custom too, cut to fit your specific opening rather than bought off a shelf.

Two honest caveats before you order anything. The framing rules above are general guidance, not brand- or region-specific instructions, and the right overlap shifts with media thickness and mounting method — a thin photo print tolerates 1/8 inch where a thick mounted canvas may want more.

Your final check is simple: place the print face-down over the mat opening. If a clean 1/8 to 1/4 inch of mat covers every edge, the sizes are right. If any paper shows, widen the overlap and recut the mat, because the frame opening itself is fixed.

One last note on the frame itself — measure from the back, verify the opening is genuinely 27 x 20 inside the rabbet, and confirm there’s enough depth for your glass-mat-backing stack. That measurement, taken once and taken correctly, is what every other number in this article depends on.