How much moulding waste should I allow for mitre cuts?

Allow 40-60mm extra per piece for mitre waste. Each 45-degree mitre cut removes a triangle of material equal to the moulding width, and you lose a saw kerf width at each cut. The calculator defaults to 50mm total waste per piece, which is sufficient for most moulding widths.

How wide should the mat (mount) be?

Standard mat width is 50-65mm. For smaller artworks (under A4), 40-50mm is appropriate. For larger pieces, 65-80mm provides better visual framing. Some framers make the bottom mat slightly wider (10-15mm more) than the other three sides for visual balance — this is called a weighted mat.

What size glass do I need?

The glass is the same size as the mat board — it sits on top of the mat inside the rabbit of the moulding. The calculator gives you the exact glass dimensions. For valuable artwork, consider UV-filtering glass or museum glass. Standard picture framing glass is 2mm thick.

What is the rabbit in picture framing?

The rabbit (or rebate) is the step cut into the back of the moulding that holds the glass, mat, artwork and backing. A typical rabbit depth is 8-12mm. Make sure the combined thickness of your stack (glass 2mm + mat 1.5mm + artwork + backing 3mm) does not exceed the rabbit depth.

How do I calculate mat opening size?

The mat opening is slightly smaller than the artwork — typically 3mm smaller on each side. This 3mm overlap holds the artwork in position behind the mat and prevents the edges from showing. So for a 200 × 300mm artwork, the mat opening would be 194 × 294mm.

WoodCalcs

Picture Frame Calculator — Moulding, Glass & Mat

Calculate moulding lengths (with mitre waste), glass size, backing board and mat board dimensions for picture framing.

Artwork Width

Width of the artwork or photo

Artwork Height

Height of the artwork or photo

Mat (Mount) Width

Width of the mat border. 0 for no mat.

Moulding Width

Face width of the frame moulding

How We Calculate This

This calculator works out all dimensions for a picture frame from the artwork size, mat width and moulding profile.

How dimensions are calculated

Mat board: Artwork size + (2 × mat width)
Mat opening: Artwork size - (2 × 3mm overlap)
Glass & backing: Same size as mat board
Outer frame: Mat board + (2 × moulding width)
Moulding per piece: Outer dimension + mitre waste

Mitre waste

Each moulding piece requires extra length for the 45° mitre cuts at each end. The default allowance is 50mm per piece which covers the mitre geometry plus saw kerf.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Always verify measurements and material quantities before cutting or purchasing.