Clear geometry.
Visible limits.

One rectangular opening.

The model covers a flat rectangular paper sheet behind one rectangular window in a rectangular board. Width is left-to-right and height is top-to-bottom in the chosen orientation. Coverage and borders are non-negative distances. It does not model curved or multiple openings, bevel depth, cutting face, material deformation, tolerances or mounting.

Formulas you can check.

The paper’s left position on the board is left border − left coverage; its top position is top border − top coverage. Checking each opposite edge rejects a sheet that would extend beyond the board. This is a placement check, not a clearance or fit specification.

Protected-area intersection.

Represent the protected rectangle by its four insets from the paper edges. Its visible width is the overlap of its left/right interval with the window interval; visible height is the equivalent top/bottom overlap. Negative overlaps become zero. Visible fraction = overlap width × overlap height ÷ protected-rectangle area.

For paper width W, protected left/right insets IL/IR and coverage CL/CR, the overlap width is max(0, min(W − IR, W − CR) − max(IL, CL)). Use the analogous formula for height. A completely enclosed rectangle is “within the mathematical opening.” A boundary match includes no practical allowance. The fraction concerns the bounding rectangle, not ink or visual importance.

Units, limits and precision.

One international inch is exactly 25.4 mm; one centimetre is 10 mm. Calculations use millimetres internally. Inputs accept non-negative decimals, simple fractions and mixed fractions. Non-zero input measurements must be at least 0.01 mm and no larger than 3000 mm. Paper, board, resulting windows and protected rectangles must be positive; window and protected-rectangle dimensions must also be at least 0.01 mm. These are software boundaries, not supplier capabilities or material limits.

Results display at most four decimal places in the selected unit. That rounding is not cutting accuracy. Unit conversions retain approximately 12 significant digits in the form, rather than repeatedly converting the rounded result. Small floating-point differences below 0.0000001 mm are treated as boundary equality for geometric checks. Real measuring and manufacturing tolerances are separate.

Independent planning, no product endorsement.

Supplier examples illustrate differing size language as checked on November 6, 2026. They are not universal overlap or fit requirements, and policies can change. Preservation references concern their stated paper/photograph contexts. Mat & Margin does not certify framing safety, recommend a board brand, sell materials or receive an affiliate payment through these links.

Measurements stay in page memory.

There is no account, upload, analytics script or saved-project database. The calculators run in your browser. Tool-to-tool links use a URL fragment to carry dimensions locally; fragments are not included in the HTTP request. Downloaded text is created on your device. If you share that full link or file, you share the dimensions it contains.

Reloading a page without a measurement fragment restores example inputs; unsaved changes are lost. Hosting infrastructure receives ordinary page requests and may process connection data under its own service policies. We do not claim the hosting provider has no logs. External source links lead to sites with their own policies.

Review and boundaries.

Content and formulas checked November 6, 2026. Worked cases are hypothetical and diagrams are original code-generated schematics, never photographs or proof of a real cut. The homepage studio image was generated as an illustration for this site; it does not document a frame, artwork or measurement we handled. Its role is visual context. Material shadows on diagrams are illustrative and do not certify physical depth or fit. Tests can verify calculation behavior under specified inputs; they cannot establish material quality, real-world manufacture or user acceptance. Confirm the current final specification with your supplier before an irreversible order.

Source: https://mat-and-margin.pages.dev/method/