How to Choose a Picture Frame: Sizes, Mats, and Materials Explained | Measure First, Then Buy

Measure the artwork’s actual image area first, then pick a frame that fits it directly or a larger one sized for a mat.

A frame bought on looks alone usually comes home wrong. The stated size is often the opening or mat window, not the outside of the frame, so an 11 × 14 frame can swallow a print you measured at the paper’s edge. Get the order right — measure, decide on a mat, then match materials to what you’re hanging — and the frame lasts as long as the picture.

What Size Frame Do You Actually Need?

Measure the image itself, width and height in inches, and note the orientation. Common US photo sizes run 4 × 6, 5 × 7, 8 × 10, and 11 × 14 inches, but a labeled size on the paper is not the same as the image area you want to show.

A frame’s advertised size typically describes the opening it is built to hold, not its outer dimensions. Confirm both the opening and the rabbet — the recessed lip the package sits against — before you buy. If you’re matting the piece, add artwork size plus mat borders plus a little clearance. The Library of Congress’s matting guidance gives a worked example: a 16 × 20-inch mat fits a 16⅛ × 20⅛-inch frame, leaving roughly ⅛ inch for expansion and contraction.

That ⅛-inch allowance is the number most people skip, and it’s the one that keeps a tight package from buckling. For multiple openings or odd dimensions, order a custom mat and verify the rabbet is wide and deep enough for mat, glazing, backing, and spacers together.

Do You Need a Mat, and Which Kind?

A mat is a board with a window cut around the artwork. It supports the piece, adds visual breathing room, and keeps the surface from touching the glazing — the last job being the one that prevents real damage.

Typical mat borders run 2–3 inches, though the right proportion depends on the artwork and frame. For anything you care about preserving, the Library of Congress specifies 100% cotton rag or chemically purified, lignin-free wood-pulp matboard, pH-neutral or slightly alkaline at pH 8.5, and a minimum thickness of four-ply. Its minimum preservation package pairs a four-ply window mat with a four-ply backmat, which creates about 1/16 inch of space in front of the artwork.

The word “archival” alone tells you nothing — the Library of Congress notes the term has no standard definition. Check for acid-free, lignin-free, 100% rag construction, and for photographs, compliance with the Photographic Activity Test (P.A.T.). Skip unpurified wood-pulp paper matboard in preservation work; it can contaminate what sits next to it.

Which Frame Materials and Glazing Hold Up?

Wood suits traditional and decorative settings; metal is chemically stable and works well in preservation packages. Both are fine when the full package is supported and protected, so the choice comes down to the look you want and one hidden detail.

That detail is the wood rabbet. Line it with a barrier film — aluminum or polyester tape with acrylic adhesive — so acids don’t migrate into the mat package. For glazing, use UV-opaque acrylic in preservation framing, and choose anti-static acrylic when the piece has friable media like pastel, charcoal, or flaking paint. Plain polyester near those materials can build a static charge and lift pigment right off the surface.

Depth is the quiet constraint. The frame has to swallow glazing, mat, artwork, backing board, moisture barrier, and securing hardware. A preservation backing can be acid-free corrugated board paired with a metalized polyester or polyester film moisture barrier, at a minimum 3 mm thick. Once assembled, the package should sit about ⅛ inch smaller than the rabbet and be held with pins or brads rather than tape. If you’d rather compare finished options than build one, this roundup of five picture frames worth checking saves the legwork.

What Do People Get Wrong When Framing?

Most framing failures trace back to nominal sizes and cheap materials, not bad taste. The Library of Congress’s matting guidance flags the recurring ones, and each is easy to avoid once you know it.

• Buying by stated size without checking the opening, rabbet, or package depth.
• Measuring the paper’s outer edge and forgetting the mat window hides part of the image.
• Letting artwork touch glass or acrylic, which invites adhesion and condensation damage.
• Using ordinary cardboard, acidic wood, unpurified paper matboard, pressure-sensitive tape, or unidentified adhesives near valuable work.
• Trusting “archival” as a guarantee instead of verifying composition and P.A.T. status.

One more: paper originals shouldn’t hang in permanent display. The Library of Congress recommends limiting light exposure and displaying a copy instead, keeping the original stored. Library of Congress matting and framing guidance spells out the material specifications behind every point above — worth reading before you buy anything destined for a valued piece.