Frame dimensions, explained
Learn which rectangle a measurement describes before comparing two frames.
| Artwork size | The full physical sheet or object, including any printed white border. |
|---|---|
| Image area | The part of the artwork carrying the picture; it may be smaller than the sheet. |
| Mat opening | The window cut out of a mat (UK: mount). It can cover part of the artwork. |
| Frame opening / nominal size | The named artwork or board size a frame is intended to receive. Verify the actual back opening. |
| Visible opening | What can be seen from the front, after the frame lip and mat overlap. |
| External frame dimensions | Outside edge to outside edge. Use these for a gallery-wall layout. |
| Rabbet / rebate | The recessed channel at the back. Its width, depth and allowances are product-specific. |
Worked example: nominal versus external
For a simplified frame with an 11 × 14 inch back opening, a ¼ inch lip overlap per edge and a 1 inch face width, the visible opening is 10.5 × 13.5 inches. The modeled outside dimensions are 12.5 × 15.5 inches.
Visible = back opening − 2 × lip overlap
Outside = visible + 2 × face width
This is geometry for one simplified profile, not a universal sizing rule. Decorative edges, allowances and non-rectangular profiles can change the result. Use the actual outside dimensions from the manufacturer for the gallery-wall planner.
Allowance is not overlap.
Allowance is extra room in a manufactured opening. Overlap is coverage at the front edge. Rebate depth is another dimension entirely. We leave unknown product tolerances and depths unspecified rather than adding a universal clearance.
US and UK labels
US “rabbet” and UK “rebate” refer to the recessed frame channel; “mat” and “mount” often refer to the window board. “Frame opening” can refer to the front visible opening or back recess in different listings. Check the supplier’s drawing.
A visual size estimate. Verify the actual artwork, frame, mat, glazing, hardware, wall and manufacturer specifications before buying or arranging a display. Dimensions alone do not guarantee fit.