A picture frame’s labeled size usually describes the artwork or components it accepts, not its outside edges. A mat adds two more measurements: the size of the whole board and the smaller window cut into it. Keep those numbers separate before ordering a replacement.
Begin with the object you want to preserve. Are you buying a frame for an unmatted photograph, replacing the mat in a frame you already own, or moving an existing matted picture into another frame? Each job starts from a different measurement.
Measure the artwork first
Lay an ordinary unmounted print flat on a clean surface. Measure its full width from left to right and its height from top to bottom, keeping the ruler straight rather than following a diagonal. Record width × height and the units. If fractional inch marks are unfamiliar, use the site’s tape-measure guide before rounding a measurement.
Measure the paper as well as the printed image when a photograph has a white border. Note which parts must remain visible, including a signature or a caption near an edge. Those details affect the window you need, even when the paper itself is a standard size.
A stretched canvas, shadow box, or unusually thick object needs depth information too. This flat-print procedure does not establish whether a frame can hold those objects. For a valuable, fragile, or already secured original, ask a framer to measure it without disturbing its mounting.
Find the fitting size of an existing frame
Place a manageable frame face down on a padded, clear surface. If its backing is designed to open and can be removed safely, examine the space where the glazing, mat, artwork, and backing sit. The recessed ledge around that space is called the rabbet. Its width and height determine the fitting area; its depth limits the stack of materials it can hold.
Measure the existing mat’s outside edges or an intact removable backing board, then check those dimensions against the recess. Do not use the outside molding dimensions as the replacement-mat size. The visible opening at the front is smaller than the fitting space because the frame lip covers the component edges.
For example, a frame can accept an 11 × 14-inch mat even though its outer molding makes the whole frame larger. The frame’s decorative width does not get added to the mat order. Confirm the actual components rather than assuming an unmarked secondhand frame follows a standard size.
Leave sealed frames, heavy glazing, broken glass, and unfamiliar retaining hardware to a framer. There is no benefit in taking apart a frame merely to obtain an outside-wall measurement.
Separate the mat board from its window
The mat’s outer width and height fit the frame. Its window determines how much of the picture shows. A listing that says “11 × 14 mat for an 8 × 10 photo” may describe the board and intended photo size while using a slightly smaller actual window. Read all three dimensions.
Overlap varies by supplier. Frame It Easy describes its usual overlap as ¼ inch on each side; American Frame’s measuring guidance describes a mat overlap of ⅛ inch per side. Both account for overlap in their ordering systems. Follow the specific order form instead of subtracting an allowance twice.
As a worked example, an 8 × 10-inch print overlapped by ¼ inch on every side has a 7½ × 9½-inch visible window. The calculation subtracts ½ inch from each full dimension, since two opposite edges are covered. That example is not a universal cutting specification.
A border or signature close to the edge may require a different opening or mounting arrangement. Tell the supplier what must show and provide the paper size separately. Enlarging the window without a suitable mounting plan can leave the backing visible around the print.
Send an order that identifies every measurement
Write separate labeled lines for artwork width × height, mat outside width × height, actual window width × height, and frame fitting depth when relevant. Add a note identifying portrait or landscape orientation and any detail that must remain visible. A photograph of the existing arrangement helps explain the job, but does not replace the dimensions.
For a replacement mat, ask whether the seller wants the intended artwork size or the exact cut-window size. For a frame that will reuse an existing mat, give the mat’s outside dimensions. Confirm any fitting allowance with the maker before submitting the order; a tolerance built into one supplier’s process need not apply to another.
