Mount Opening Calculator — Weighted Bottom Border

A weighted bottom border is slightly larger than the top and sides (typically 15% larger). This compensates for an optical illusion that makes equally-sized borders appear to have a smaller bottom. The weighted bottom looks visually balanced.

Standard overlap is 5 mm on each side — the mount covers 5 mm of the artwork edge. This hides rough edges, tape marks and uneven borders. For prints with printed borders, reduce overlap to 2-3 mm.

Standard mount borders are 50-80 mm. For small works (under A4), use 50-65 mm. For medium works (A4-A3), use 65-80 mm. For large works, 80-100 mm. The border should be proportional to the artwork — not too narrow or too wide.

The mount opening is cut at a 45-degree angle (bevel). The bevel reveals the white core of the mount board, creating a subtle frame around the artwork. A good bevel cut is the mark of professional framing.

Weighted bottom borders are traditional and recommended for most framing situations. Equal borders can look bottom-heavy due to the optical illusion. Only use equal borders for very modern, minimalist presentations.