Methodology

Reference data

The size references describe nominal artwork or paper dimensions. Sources explain the definitions and manufacturer-specific sizing conventions, and review dates show when we checked them. A-series dimensions refer to paper; inch sizes are nominal examples for comparing frames and prints.

Unknown mat openings, actual visible openings, external frame dimensions, rabbet depth and manufacturer allowances are left unspecified. They cannot be inferred from a nominal label.

Calculation rules

• Unit conversion uses exactly 25.4 millimeters per inch. We round the displayed values after completing the calculation.
• A mat window subtracts twice the per-edge overlap from the full artwork width and height.
• Centered board-edge borders are half the difference between the board and window in each direction.
• Frame suggestions satisfy the requested minimum border and full-sheet dimensions, testing both orientations and sorting by nominal area. Results are not merchant inventory.
• Aspect-ratio matching compares the entered orientation. Fill uses the larger scale factor; fit uses the smaller. Crop and blank percentages describe area.
• Gallery layouts use actual outside frame dimensions. Gaps run between outside edges. Negative side space means the layout exceeds the available visual width.

Diagrams and precision

Rectangles are proportional; line thickness, labels and dimension ticks are illustrative. A dark border is a diagram outline unless explicitly described otherwise. Display rounding is not a manufacturing tolerance.

Review and correction

A review checks cited definitions, formulas, worked examples, invalid inputs and related pages. We update affected records and page dates when substantive information changes. The date does not imply that every manufacturer’s current product has been measured.

Report a reproducible error. We review the original source, reproduce the calculation, correct all affected outputs and record material changes.