Measure the complete package
A framed picture is a set of nested rectangles. The image sits on a sheet; a mat may cover some of the sheet; the frame surrounds the mat and holds the glazing and backing. A size written on a listing may refer to only one of those rectangles. Read the product specification and ask which measurement it describes.
Start with four separate measurements: the visible image area, the paper, the proposed mat opening and the outside of the frame. Add the frame depth if it matters beside furniture or within a shelf. Do not assume that a label such as “for an 8 × 10 print” tells you the complete outside size.
Use border arithmetic before shopping
For a simple illustration, an 8 by 10 inch image with a 2 inch border on every side occupies a 12 by 14 inch rectangle. The width is 8 + 2 + 2, and the height is 10 + 2 + 2. That example shows why a mat changes the space required; it is not a frame-order specification.
An actual mat opening can overlap the print edge, and the sheet can be larger than the visible image. A frame also covers an edge of the package. Give your measurements to the framer and ask for the final visible opening and outside dimensions before ordering.
Ask about materials as well as appearance
A mat provides a visual margin, but framing materials also affect how a paper object is supported. The Library of Congress describes preservation framing as a way to limit environmental risks and recommends stable materials and separation between the object and glazing. For an original or a valuable print, discuss the complete package with a qualified framer or conservator.
For a reproduction, you can still make informed choices about the mat, backing and glazing. Ask what the materials are and how the print will be held. Keep the answers with the order instead of treating a single marketing word as a complete description of the framing method.
Check the result in the room
Compare a paper outline of the outside frame with the space you measured. Then compare the border width against the actual composition. A dense image may feel different with a wide mat than a simple line drawing does. You can test the relationship with inexpensive paper before committing to the final materials.
Think about the conditions in the display location. Avoiding direct sunlight and obvious sources of heat or moisture is a sensible starting point, and valuable works deserve advice tailored to their materials. A frame changes presentation; it does not remove the need to consider the environment.