Calculator
Enter artwork size first. Choose a method: calculate borders from an outer mat size, or calculate outer size from your borders.
Formula used
The window is cut slightly smaller than the artwork, so the mat holds the edges.
- OpeningWidth = ArtworkWidth − 2 × Overlap
- OpeningHeight = ArtworkHeight − 2 × Overlap
Borders are the distances from the mat edge to the window.
- OuterWidth = OpeningWidth + LeftBorder + RightBorder
- OuterHeight = OpeningHeight + TopBorder + BottomBorder
- BottomBorder = TopBorder + BottomWeight (when enabled)
Offsets tell you where to draw the four lines that form the window.
- LeftLine = LeftBorder
- RightLine = OuterWidth − RightBorder
- TopLine = TopBorder
- BottomLine = OuterHeight − BottomBorder
How to use this calculator
- Measure the artwork width and height you want to mount.
- Pick units, then set an overlap that suits mounting.
- Select a method: outer size first, or borders first.
- Choose equal borders, or enter custom border values.
- Enable weighted bottom if you prefer traditional balance.
- Press Calculate, then mark cut lines using offsets.
- Download a CSV or PDF to keep project records.
Example data table
Sample values to help you sanity-check your inputs.
| Artwork (W×H) | Overlap | Outer mat (W×H) | Borders (L/R/T/B) | Opening (W×H) |
|---|---|---|---|---|
| 8 × 10 in | 0.125 in | 14 × 18 in | 3 / 3 / 3.875 / 4.375 in | 7.75 × 9.75 in |
| 20 × 30 cm | 0.3 cm | 30 × 40 cm | 5 / 5 / 4.4 / 5.4 cm | 19.4 × 29.4 cm |
| 6 × 6 in | 0.125 in | (borders method) | 2 / 2 / 2 / 2.5 in | 5.75 × 5.75 in |
Note: the first row uses weighted bottom with a 0.5 in weight.
Opening size and overlap control
Mat openings should hold the artwork securely without hiding key detail. This calculator subtracts a chosen overlap from each edge, so the visible window equals artwork width minus two overlaps, and height minus two overlaps. For photographs, 0.125–0.25 in overlap is common; for delicate botanical prints, keep overlap minimal and use archival hinges.
Border proportions for visual stability
Even borders look modern, but a slightly heavier bottom often feels balanced when hanging. With weighted-bottom mode, the tool adds extra border to the bottom while keeping left, right, and top consistent. If you are framing garden illustrations with tall stems, consider a modest weight so the composition does not appear to float upward.
Outer mat size planning
When you enter an outer mat size, the calculator checks whether your borders and opening can fit. This prevents designs that exceed the board, especially when you use wide borders for dramatic negative space. If you prefer to set borders first, the tool can also compute the outer dimensions, helping you choose a standard frame size. It simplifies bulk material ordering.
Tolerances and cutting workflow
Accurate cuts depend on consistent measuring. Use the same unit system throughout and verify that all values are positive. Allow a small trimming margin if your board edges are not perfectly square. After calculating, mark the opening offsets from each side, double-check diagonals, and cut with a sharp blade to avoid ragged bevels. For thick boards, score lightly first, then finish with two firm passes.
Documentation and repeatable results
Garden-themed framing often involves series work: seasonal photos, seed packet collages, or pressed-flower displays. Exporting CSV keeps a clean record of sizes, borders, and overlap for each piece, while the PDF provides a quick reference in the workshop. Label each file with crop, date, and frame size, and store notes on glass type and backing. Keeping these records reduces waste and makes future re-mats faster and consistent.
FAQs
What overlap should I use?
Use enough overlap to hide edges and hold the piece. Typical overlap is 0.125–0.25 in per side. For thin paper or pressed flowers, reduce overlap and rely on archival hinges or corners.
Why does the bottom border look larger?
A weighted bottom helps the artwork appear visually centered when displayed. The calculator adds extra border only to the bottom, while keeping left, right, and top equal, unless you choose fully custom borders.
Can I design from a standard frame size?
Yes. Enter the outer mat size that matches your frame and set your border style. The tool will confirm the opening fits, then return the opening size and the exact border values to mark on your board.
What if my borders do not match the outer size?
In custom mode, the calculator validates that left+right+opening equals the outer width and top+bottom+opening equals the outer height. If it fails, adjust a border, overlap, or outer size until the geometry balances.
Should I cut exactly to the calculated opening?
Cut to the calculated opening for the visible window, but measure twice and test on scrap first. Blade angle, board thickness, and bevel depth can change the apparent opening slightly, so consistent technique matters.
How do the CSV and PDF exports help?
CSV is best for tracking many projects and reusing dimensions. The PDF is a clean one-page shop sheet showing inputs and outputs. Together they reduce mistakes, support repeat orders, and speed up future mat layouts.