What is a weighted bottom border?

A weighted bottom border is slightly wider than the top and sides, typically 10-15 mm extra. This compensates for an optical illusion that makes equal borders look bottom-heavy. It is standard practice in professional framing.

What is a standard mat border width?

Standard mat borders are 55-75 mm (2.2-3 inches). For small works under A4, 55 mm works well. For larger pieces, 65-75 mm gives better visual balance. Very large works may use 100+ mm borders.

Why does the opening overlap the artwork?

The mat opening is cut slightly smaller than the artwork (3 mm overlap each side) so the mat edges hold the artwork in place and no gaps are visible. This overlap is standard in professional framing.

ArtCalcs

Mat Board Calculator — Dimensions & Opening Size

Work out mat board dimensions and opening size with correct border widths.

Artwork Width

Artwork Height

Border Width

Width of top and side borders

Weighted bottom border

Add extra width to bottom border for visual balance

Bottom Extra

Extra width added to bottom border

Price per Mat Board (optional)

How We Calculate This

Opening = Artwork size - 6 mm (3 mm overlap each side)

Mat board = Opening + (2 x Border width) horizontally, and Opening + Top border + Bottom border vertically.

When the weighted bottom is enabled, the bottom border is increased by the extra amount you specify, giving a visually balanced appearance.

Frequently Asked Questions

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Calculate mount opening dimensions with weighted bottom border and artwork overlap allowance for professional picture framing results.

Last updated: February 2026

All calculations are estimates. Always verify quantities before purchasing materials.