Picture Frame Calculator
Enter your artwork size, mat border width, and frame molding width to get every dimension you need for a perfect custom frame: mat opening, inner frame size, outer frame size, glass (glaze) area, and total molding length for purchasing. Switch between inches and centimetres at any time.
What does a picture frame calculator work out?
A picture frame calculator takes four key measurements - artwork size, mat border widths, molding width, and rabbet depth - and returns all seven dimensions needed to cut, buy, and assemble a custom frame. The mat opening is the bevel-cut window that exposes the artwork. The inner frame (also called the rabbet opening) is the internal cavity that holds the glass, mat, and artwork. The outer frame is what hangs on the wall. The glaze dimensions tell you how large to cut the glass or acrylic. The molding length tells you how many linear feet of frame profile to buy, including enough for four mitered corners and corner waste.
How to measure your artwork and choose mat borders
Measure the artwork itself, not the paper it is printed on if it has a white border. For photographs with bleed-to-edge printing, measure edge to edge. Mat borders are the visible strips of mat board between the artwork and the frame. A classic starting point is 2 in (5 cm) on the sides and top, with 2.5 in (6.5 cm) on the bottom. The extra bottom space, sometimes called the "museum bottom," creates optical balance because the eye perceives a centred mat as slightly top-heavy. For larger artwork, scale the borders proportionally: a 16 x 20 in print often looks best with 3 in sides and 3.5 in bottom. The mat overlap is the small amount (typically 0.25 in / 6 mm) by which the mat edge covers the artwork, hiding the artwork edge and preventing it from slipping through the opening.
Understanding molding width and rabbet depth
Molding width is the visible face of the frame profile, measured from the inner edge to the outer edge. Narrow profiles (0.75-1 in / 2-2.5 cm) give a modern, minimal look. Medium profiles (1.5-2 in / 4-5 cm) are the most common for fine art. Wide or ornate profiles (2.5 in+ / 6 cm+) suit large traditional paintings and diplomas. The rabbet is the L-shaped ledge milled into the back of the molding where the glass, mat, and artwork stack. Most commercial moldings have a rabbet of 0.25-0.375 in (6-10 mm). The inner frame dimension reported by this calculator is the rabbet opening size, which is what the mat and glass must fit into.
How to use the molding length to buy supplies
The calculator adds up 2 x (outer width + outer height) to get the minimum perimeter, then adds 4 x molding width to account for the waste cut off at each of the four mitered corners. This is the minimum length of molding to order. In practice, add 10-15 percent as a safety margin for measurement errors and any miscut. Frame molding is usually sold by the linear foot or metre. Divide the molding length by 12 if working in inches to convert to feet, or simply read the cm figure directly. For a standard 8 x 10 in artwork with 2 in mat borders and 1.5 in molding, you need about 68 in (5.7 ft / 173 cm) of molding.
Standard photo and print sizes vs. typical mat and frame
| Artwork size | Mat opening | Inner frame | Typical stock frame |
|---|---|---|---|
| 4 x 6 in | 3.5 x 5.5 in | 8 x 10 in | 8 x 10 in |
| 5 x 7 in | 4.5 x 6.5 in | 9 x 11.5 in | 9 x 12 in |
| 8 x 10 in | 7.5 x 9.5 in | 12 x 14.5 in | 12 x 16 in |
| 11 x 14 in | 10.5 x 13.5 in | 15 x 19 in | 16 x 20 in |
| 16 x 20 in | 15.5 x 19.5 in | 20 x 25 in | 20 x 24 in |
| 18 x 24 in (poster) | 17.5 x 23.5 in | 22 x 29 in | 22 x 28 in |
| 24 x 36 in (poster) | 23.5 x 35.5 in | 28 x 41 in | 24 x 36 in |
Common artwork sizes with the most widely stocked standard frame sizes. Mat borders assume 2 in sides and top, 2.5 in bottom. All values in inches.
Frequently asked questions
What is the difference between the mat opening and the inner frame size?
The mat opening is the bevel-cut window in the mat board through which you see the artwork. It is intentionally smaller than the artwork by the mat overlap on each side (typically 0.25 in), so the mat edge covers and holds the artwork. The inner frame size (rabbet opening) is the full internal cavity of the assembled frame, which equals the outer dimensions of the mat board, not the cut window.
Why is the bottom mat border wider than the sides and top?
Because of a perceptual illusion: when all four borders are the same width, the bottom appears smaller than the top, making the artwork look like it is falling out of the frame. Adding an extra 0.25-0.5 in (0.5-1.5 cm) to the bottom border corrects the illusion and gives the image a stable, grounded look. This technique is called the "museum bottom" or "weighted bottom."
How do I calculate how much molding to buy?
Add the outer width and outer height, multiply by 2 to get the perimeter, then add 4 times the molding width for the corner waste from 45-degree miter cuts. Add a 10-15 percent overage for safety. This calculator does all that automatically and shows you the total in your chosen unit.
What size should the glass or acrylic be?
The glass dimensions in this calculator match the inner frame size. In practice, the glazing is often cut 1/16 in (1-2 mm) smaller on each side so it drops into the rabbet without binding. Ask your glass cutter to trim it to the inner frame dimensions and they will account for the fit tolerance.
Can I use this calculator for frames without a mat?
Yes. Set all three mat border fields to zero. The mat opening will then match the artwork size minus the overlap, and the inner frame will equal the artwork size. You may also want to set the mat overlap to zero if you are not using a mat at all, in which case the inner frame and mat opening are both equal to the artwork dimensions.
What is a rabbet and why does it matter?
The rabbet (also spelled rebate) is the recessed ledge on the inside back edge of the frame molding. It is where the glass, mat board, artwork, and backing board stack up and are held in place. The rabbet depth is usually 0.25-0.375 in (6-10 mm). If your stack of materials is thicker than the rabbet depth, the frame will not close properly, so choose a molding with a deep enough rabbet for your materials.