How to Measure for a 20 x 28 Poster Frame: Sizing and Fit Guide?

A rolled poster fights you: measure it while curled and your width can read a quarter-inch wide — the difference between a print that drops into a frame and one that buckles. Lay it flat on a hard, clean surface (table or countertop, never carpet, a bed, or a curved rug, which let the paper sag). Smooth it with your hands, then measure full width and height edge to edge with a metal ruler or tape measure. Write the numbers down, then measure both again. If the second pass disagrees, the poster is still distorted and needs more time flat.

What Size Is A 20 x 28 Poster Really?

That gap is normal. This is why frame-size charts from Frame USA and Custom Picture Frames treat 20 x 28 as a custom size rather than a stock poster size. The standard poster dimensions those charts list are 18 x 24, 24 x 36, and 27 x 40. Anything outside that trio, including 20 x 28, tends to push you toward custom framing.

If you’re ordering a frame after measuring, our roundup of the best 20 x 28 poster frames we tested covers which options accept that measurement without a mat.

How To Measure When a Mat Is Involved

A mat changes the math twice over. Size the frame to the framed-and-matted dimension, and cut the mat opening to the bare print size — two separate numbers, and mixing them up is the most common framing mistake.

The frame is generally one to two inches wider than the poster when a border or mat is included. If your poster measures 19 3/4 x 27 1/2 and you want a two-inch mat border, you’re shopping for a frame in the 24 x 32 range, not a 20 x 28. Order the frame first and the mat opening second, and confirm the opening matches your measured print — not the advertised size. Adobe’s poster framing guide makes the same point: work from the final framed-and-matted dimensions, never from the bare poster.

Why The Frame Lip Eats Your Edges

That’s usually fine, but it hides a title, date, or signature sitting close to the outer edge. Before committing, lay the poster on the frame’s backing board and see what falls outside the opening. If anything you care about is within a quarter inch of the edge, order a slightly larger opening or accept it will be trimmed from view. A mat earns its keep here: it holds the print away from the lip and keeps the full image visible, at the cost of a bigger frame.

One more check: confirm whether the frame is sold as a 20 x 28 or as a 20 x 28 mat opening — not the same thing. Frame USA’s sizing chart and Custom Picture Frames’ standard-size reference both lay out the distinction between print size, opening, and outer frame dimension.

FAQs

Should I measure my poster before or after flattening it?

Always after. A rolled poster holds tension that widens one dimension and narrows the other, so measuring while it curls gives numbers that won’t match the relaxed paper. Unroll it, lay it on a hard flat surface, and let it settle before measuring.

Do I order the frame in the poster’s size or the mat’s size?

The frame takes the mat’s outer dimension; the mat opening takes the poster’s measured dimension. Two different numbers. If you order a frame to match your print and then add a mat, the mat will cover artwork. Size the frame to the framed-and-matted total instead.

Is 20 x 28 a standard frame size in the US?

It appears in frame-size charts, but as a standard or custom frame size rather than a common poster size. The widely stocked poster dimensions are 18 x 24, 24 x 36, and 27 x 40. Expect to order custom for a true 20 x 28, and measure your print before you do.