MetraNestTwo sizes to keep separate
The outer size refers to the mount board that fits inside the frame. The opening is the window through which the picture appears. The outside dimensions of the frame moulding are not the mount board size. Use the frame’s stated usable internal dimensions.
Calculate a centred border
The difference between the outer width and the opening width is divided by two, for the left and right borders. Do the same for the height. If the picture and frame proportions differ, the horizontal and vertical borders will have different widths, even with a perfectly centred picture.
Check the image that will actually be visible
Enter the image size and the overlap wanted on each edge. The tool subtracts two overlaps from each dimension to obtain the visible opening. Check whether the seller states the compatible picture size or the actual cut opening. Overlap may hide a detail near the edge.
Opening = image dimensions − 2 × overlap. Left and right borders = (outer width − opening width) ÷ 2. Apply the same calculation to the heights for the top and bottom.
A picture in a larger format
A 20 × 30 cm picture with 0.3 cm overlap per edge gives a 19.4 × 29.4 cm opening. In a 30 × 40 cm mount board, all four borders are then 5.3 cm wide.
Details to check
- Keep the photo size, actual opening and outer size separate.
- Check portrait or landscape orientation.
- Check that important parts near the image edges remain visible.
Frequently asked questions
Can the bottom border be wider?
Yes, but this calculation uses geometric centring. A mount with a wider bottom border requires a different division between the top and bottom borders.
Why do two borders differ when the image is centred?
Centring makes the left and right borders equal, and the top and bottom borders equal. It does not make all four sides the same width.
Method and references · Editorial review: 25 October 2026
The geometric formulas are explained here. For a product, its packaging dimensions and coverage rate remain the reference inputs.