Picture Frame Calculator — Mat, Glass & Molding Size

Formula

How this is calculated

A picture frame has three main material components: the mat board (a flat border that surrounds the artwork and creates visual breathing room), the glass or acrylic glazing (cut to the mat outer size), and the molding (the decorative timber or metal profile that forms the visible frame edges).

The mat outer size equals the artwork dimensions plus twice the mat border width on each side. Glass, acrylic and backing board are all cut to this same mat outer size — it is also the size you specify when buying pre-cut glass from a framing supplier. The frame molding then assembles around the mat: the frame outer size equals the mat outer size plus twice the molding face width on each side.

The molding is bought by linear length. The raw perimeter needed is 2 × (mat outer width + mat outer height), giving four pieces (two of each dimension) cut at 45° miter joints. A 10% waste allowance is included for the diagonal cuts — professional framers often allow up to 15% for complex moulding profiles; reduce to 5% if you are cutting carefully from a single long length. Note: traditional framing uses a small mat overlap (typically 3–6 mm or ⅛–¼ in) to prevent the artwork slipping through; subtract your chosen overlap from the artwork dimensions before entering them if this applies.