Start with the physical sheet.
Lay out the dimensions of the actual paper or photograph, edge to edge. Record width from left to right and height from top to bottom in the orientation you intend to display. A print sold as 8 × 10 may have an image smaller than its sheet, or may not match the nominal size exactly. Measure your own piece before ordering.
Write the unit beside the numbers. Keep all measurements in the same unit for a calculation. If using inches, our tools accept decimals, fractions such as 1/8, and mixed fractions such as 8 1/2. Measure both directions; do not infer height from a familiar aspect ratio.
Separate the image from the paper.
If there is a white border, measure where the image and any signature or edition number sit on the sheet. The edge of the printed image is not necessarily the edge of the paper. Decide which details must stay visible, then record their bounding rectangle as distances in from the four paper edges.
For example, an 8 × 10 image centered on a 10 × 12 sheet has a 1-inch white margin on each side. Covering 1 inch at every edge reaches the image boundary; covering 1 1/8 inches hides an additional 1/8 inch of the image at each edge. These are geometric descriptions, not mounting recommendations.
Name the opening explicitly.
The window is the hole in the mat. Its width equals paper width minus the left and right coverage; its height subtracts the top and bottom coverage. Coverage is a measurement at each paper edge, while a mat border runs from the window edge to the board’s outside edge. They are different distances.
An 8 × 10 sheet with 1/8-inch coverage on all four edges has a 7 3/4 × 9 3/4-inch window. If a supplier asks for art size rather than exact window size, confirm whether that supplier will make a further deduction.
Measure the board, then check the frame.
For an existing mat, record its outside dimensions separately from its opening. For an existing frame, identify the inside component space or use its properly fitting existing component as a reference. The decorative outside measurement of a frame does not tell you the mat size.
A width and height alone cannot confirm fit. The frame also needs sufficient depth for glazing, mat, artwork and backing; clearance, squareness and fixing methods need checking. Avoid opening a fragile or valuable assembly just to obtain dimensions: ask a suitable framer.
Make a usable measurement note.
Record paper width × height; important-area insets; intended coverage at left, right, top and bottom; exact window width × height; and board outside width × height. Mark the display orientation. Keep any unmeasured frame clearance or depth as an open question rather than silently assuming zero.
Use the planner to reconcile the measurements, then use the visibility check for important edge details. Before purchase, read the order form’s definition of each size and have the supplier confirm how it will interpret your note.
Sources & scope
Checked November 6, 2026. Supplier policies are examples of that supplier’s wording, not universal specifications. Geometry and worked examples are our own derivations; see method and limits.
Source: https://mat-and-margin.pages.dev/guides/measure-for-a-mat/ · Checked November 6, 2026