Picture Frame & Mat Size Calculator
Find frame and mat dimensions for your artwork, or calculate a mat to fit a frame you already own.
Your measurements
Measure the full artwork/paper. Use decimals or fractions, such as 8.5, 1/4 or 8 1/2. Examples are editable planning values, not requirements.
Extra bottom weight adds to the bottom border only and increases mat/frame height.
Only estimates the outside footprint; it never changes mat, glass or backing size. Real moulding/rabbet construction varies.
Calculations stay in this browser tab. Measurements and results are not uploaded, saved or automatically included in feedback. Refreshing clears entries.
Enter artwork and the required mat or frame measurements to see your plan.
How it works
- Measure the full artwork or paper width and height, then choose inches, centimeters or millimeters.
- For Artwork → Frame, choose a mat or no mat. With a mat, enter overlap and uniform or custom borders.
- For Existing frame → Mat, enter the inside frame/glass dimensions and overlap. Optionally add bottom weighting.
- Review the window, borders and package size. Copy the plan and check the actual frame’s fit tolerances before ordering or cutting.
A real example
Fictional framing example: 8 × 10-inch artwork with 0.25-inch overlap on each edge leaves a 7.5 × 9.5-inch mat opening. Adding 2-inch borders gives an 11.5 × 13.5-inch mat outer size and calculated frame/glass/backing size. The overlap is accounted for; simply adding borders to the full artwork would give a different result.
For an existing 11 × 14-inch frame, the same opening gives 1.75-inch left/right borders and 2.25-inch top/bottom borders. An extra bottom weight of 1 inch changes top/bottom to 1.75 and 2.75 inches, while keeping the 14-inch outer height.
Artwork, visible window and mat outer size
Measure the full sheet, not just the printed image. The opening is the visible artwork rectangle. An overlap of O per edge removes 2O from both artwork width and height; the mat covers those edges. Choose an overlap that suits your actual artwork and framing plan—this calculator does not prescribe a universal amount.
Mat borders run from the window to the mat’s outside edges. The outer size equals the opening plus the two corresponding borders. The full paper must also fit behind the mat, including at each edge; a window that fits is not sufficient if the paper extends outside the package.
What frame size refers to
The calculated frame size is the inside/rabbet/glass size used to hold the mat package. Glass and backing use that same nominal plan size. The decorative moulding’s outside edge is different. Optional moulding face width estimates the wall footprint by adding twice that width to both package dimensions, without changing the mat.
With no mat, the calculation uses the artwork size and invents no overlap. A frame lip may cover some artwork, and actual rabbets, tolerances and moulding construction vary. Confirm physical dimensions and allowances with the frame or framing provider before cutting or ordering.
Uniform and bottom-weighted mats
Artwork → Frame lets you enter equal or individual left/right/top/bottom borders. Extra bottom weight adds only to the bottom border and increases the outer height.
Existing frame → Mat centers the window by default. Bottom weighting redistributes the fixed vertical space: top = (frame height − opening height − extra weight) ÷ 2, and bottom = top + extra weight. Left/right remain centered. A negative calculated border or paper extending beyond the outer edge produces a clear does-not-fit result.
Reference frame sizes
The comparison list is 4×6, 5×7, 8×10, 8.5×11, 11×14, 12×16, 12×18, 16×20, 18×24, 20×24, 20×30, 24×30, 24×36 and 30×40 inches. This is a restrained reference list, not a claim that every retailer stocks every size. Rotated dimensions count as equivalent.
Nearest sizes are ranked by combined width/height difference, not by whether your current borders fit them. The calculator never changes your dimensions to force a match. Use Existing frame → Mat to test a different inside size explicitly.
Frequently asked questions
What size frame do I need for my picture with a mat?
Subtract the chosen overlap from each edge to get the mat opening, then add left/right and top/bottom borders. The resulting mat outer size is the nominal frame/glass/backing size, subject to actual frame tolerances.
Can I use a frame I already own?
Yes. Enter its available inside/glass dimensions and your full artwork dimensions in Existing frame → Mat. The calculator centers the opening, shows the borders and checks that the opening and full paper fit.
Can I enter fractions and change units?
Yes. Enter decimals, fractions such as 1/4, or mixed values such as 8 1/2. Inches, centimeters and millimeters convert through canonical inches. Inch results also show approximate nearest-1/16 equivalents without replacing decimal measurements.
Is a particular mat border or overlap best?
No universal choice is implied. All entries are editable planning measurements; choose them for your actual artwork and check the framing requirements.
Does moulding width change my glass size?
No. It only estimates the outside footprint. Actual moulding/rabbet construction varies; the tool does not calculate rabbet depth, glass thickness or saw cuts.
Are measurements uploaded or stored?
No. Calculations run locally in this browser tab, with no uploads required. Refreshing clears entries. Copy Results uses your clipboard or a manual-copy fallback; feedback does not automatically include measurements or results.
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