What size frame and mat do you need for a picture? Enter your artwork size to calculate the mat opening and frame insert size, or find the borders for a frame you already own. Adjust the edge overlap and add a wider bottom border if you want one.
How to use the picture frame and mat calculator
- Choose inches, centimetres or millimetres. Measure the full artwork sheet in the orientation in which you will display it.
- Enter the overlap on each edge. This is the strip of paper the mat will hide, not the width of the decorative mat border.
- To choose a frame, enter the side and top borders. To use an existing frame, enter its nominal insert size or its measured inside back recess.
- Add a bottom extra if you want the lower border wider than the upper one. If known, enter how far the frame lip covers the mat.
- Select Calculate frame and mat. Check the opening, outside mat size, four borders and diagram before ordering.
Use decimal numbers, such as 0.125 for 1/8 in, with a point or comma and no thousands separators. Changing units converts the existing dimensions. Recalculate after changing an input. The swap button rotates only the frame dimensions. It does not rotate your artwork.
What frame size do I need for my print?
Start with the actual paper dimensions. A product named after its printed image may have additional white paper around it. Measure that full sheet if you want to keep it intact. The calculator subtracts the overlap from both sides to find the visible window, then adds the mat borders to find the outside mat size.
The resulting outside mat dimensions are the nominal insert size to discuss with a frame supplier. They are not the frame's outer dimensions on the wall. For example, a frame sold for an 11 × 14 in insert has an outer size that depends on its moulding. Use the actual outer size when planning a gallery wall.
If the sheet has an uneven white margin, a signature close to an edge or an off-centre subject, equal overlap may not give the composition you want. This calculator uses the same overlap on all four edges. Choose a custom opening with a framer when different edge coverage is needed.
Mat opening, mat border and frame lip
The mat opening is the rectangular window through which the picture is seen. It is smaller than the full sheet when overlap is positive. The border runs from this window to the outside edge of the mat board. These two measurements serve different purposes.
A frame lip covers a strip around the outer edge of the mat. If a board border is 2 in wide and the lip covers 0.25 in, the visible border is 1.75 in. That deduction changes the visible border, not the mat's outside size. Do not enter the full wooden moulding width as lip coverage.
The diagram shows the mat board, window and hidden artwork edge. It does not draw a decorative frame profile. If you enter lip coverage, the result table separately gives the estimated visible borders. If the lip is unknown, no amount is silently deducted.
How much should a mat overlap a picture?
Overlap must suit the actual artwork, mounting method and cutting accuracy. The calculator starts with an editable 0.125 in on each edge. That equals 3.175 mm. Check what would be covered before using it, especially with small prints or text near an edge.
With an 8 × 10 in sheet and 0.125 in overlap per edge, the opening is 7.75 × 9.75 in. The total reduction is 0.25 in in each dimension. It is not 0.125 in overall.
A zero overlap is allowed so that you can inspect the geometry, but the result flags that the mat does not cover the paper edges. It is not a mounting plan. The tool does not support a floating display with a window larger than the sheet.
The frame and mat sizing formulas
Window width = artwork width − 2 × overlap. Window height = artwork height − 2 × overlap.
When choosing a frame, outside mat width = window width + left border + right border. Outside mat height = window height + top border + bottom border. In this tool, left and right are equal, and bottom border = top border + bottom extra.
For an existing frame, begin with the planned outside mat width and height. Side border = (outside mat width − window width) ÷ 2. Top border = (outside mat height − window height − bottom extra) ÷ 2. Bottom border = top border + bottom extra.
If you entered the measured back recess, subtract the chosen total fitting allowance once from the recess width and once from its height before using those formulas. If you entered nominal insert dimensions, no fitting allowance is subtracted.
The opening's upward shift from the mat centre is half the bottom extra. The sheet edge sits behind the mat at a distance equal to each board border minus overlap. A negative distance would put part of the paper outside the board, so the calculator rejects that layout.
Example: an 8 × 10 photo in an 11 × 14 frame
Use an 8 × 10 in full photo sheet, an 11 × 14 in nominal insert size and 0.125 in overlap per edge. Start with zero bottom extra. The window is 7.75 × 9.75 in.
The left and right borders are (11 − 7.75) ÷ 2 = 1.625 in each. The top and bottom borders are (14 − 9.75) ÷ 2 = 2.125 in each. The side borders and the top border are different because the photo and frame have different proportions.
Now enter a bottom extra of 0.5 in. The top border becomes 1.875 in and the bottom becomes 2.375 in. The opening moves up by 0.25 in. It stays the same size, and the outside mat remains 11 × 14 in. Load example uses this bottom-weighted version with lip coverage left blank.
A metric example when choosing a frame
For a 210 × 297 mm sheet, use 3 mm overlap, 40 mm side borders, a 40 mm top border and 10 mm bottom extra. The opening is 204 × 291 mm. The outside mat becomes 284 × 381 mm, with a 50 mm bottom border. These are calculated custom dimensions, not a claim that this frame size is stocked.
If you want a specific ready-made frame, switch to the existing-frame mode and enter that frame's insert dimensions. Let the calculator recalculate the borders. Simply rounding an outside dimension changes the border layout and should be checked again.
How to measure an existing frame
Find out which dimensions the seller lists. A frame's outside edge, its front viewing opening and its back recess are different measurements. A label such as 30 × 40 cm often refers to the insert it accepts. Confirm this before choosing nominal-size mode.
If you measure the recess directly, work from the back where the board sits and check both dimensions. Choose the measured-recess mode and enter the total fitting allowance your frame needs. For example, a 303 × 403 mm recess with a 3 mm total allowance in each dimension produces a planned 300 × 400 mm board. The 3 mm is deducted once per dimension, not twice.
There is no universal allowance for every frame. Check the frame maker's recommendation, squareness and the actual existing insert if available. This planner does not check the recess depth or whether glass, mat, artwork and backing will fit as a stack.
Why does the calculator say the artwork will not fit?
A window can fit inside a frame even when the full paper sheet does not. This can happen with very narrow borders or a large bottom extra. The calculator checks the full untrimmed sheet as well as the visible opening.
Increase the frame size, reduce the bottom extra or adjust the relevant board border. Do not increase overlap just to hide a physical sheet-size problem. Changing the window does not make the paper itself smaller.
Does a wider bottom border change the opening?
No. Bottom weighting changes the position and surrounding borders. In an existing frame, adding 10 mm of bottom extra reduces the top border by 5 mm and increases the bottom by 5 mm compared with the centred layout. The opening moves up by 5 mm. This tool keeps the picture centred horizontally.
Can I use this for double mats or a floating picture?
This version calculates one rectangular opening in one mat. A double mat needs a second opening and a chosen reveal. A float mount exposes the sheet edge and uses different mounting geometry. Multiple windows, oval openings, canvas stretchers, shadow boxes and moulding mitres are outside this calculation.
Are the results ready for a mat cutter?
The dimensions describe the intended finished window and board layout. They are not cutter guide settings. Bevel direction, board thickness, blade position and overcut adjustments depend on your tool and method. Follow its instructions and check a test cut before cutting the final board.
Read the printed measurements rather than measuring the screen diagram. Display values are rounded for readability, while fit checks use unrounded values. Do not round small overlaps or fitting allowances to whole centimetres.
Check the measuring method before ordering
Logan's mat measuring guide explains how the artwork, mat window and frame recess relate. Metropolitan Picture Framing's mat calculator is another manufacturer resource for framing paper art and photographs. Their entry conventions may differ, so check whether a requested measurement means paper size, window size or outside mat size.
After selecting the frame, use our gallery wall calculator to plan its position with other frames. For the rest of the room, try the paint calculator or curtain fabric calculator. The generated photo illustrates a framing project and is not a dimensioned cutting guide.
