Start with the actual paper
The overlap hides part of each edge. It is deducted from the paper, not added to the opening.
For the space around your art
Size a single rectangular mat opening from your paper and overlap. Compare centred borders, an equal border, or a deliberate offset — with a cut plan you can keep.
The overlap hides part of each edge. It is deducted from the paper, not added to the opening.
Centre within an existing mat, choose one equal border, or shift the opening to your own preference.
Copy or print the opening and all four borders. The drawing explains the layout; it is not a cutting template.