Planning a frame? Enter your artwork size, how much mat you want around it and the width of the frame moulding. The calculator gives the mat opening, the glass and backing size, the outer size of the frame and how much moulding to buy.
Frame and mat size
How it works
The mat window is the artwork size minus the overlap on each side, so the mat holds the art without covering much of it. The mat outer size is the window plus the border on both sides (plus any extra at the bottom). That is also the size of the glass and backing board.
The outer frame size adds the moulding width on every side. Moulding length is the perimeter of the glass plus about eight moulding widths, because each mitred corner uses extra.
Worked example
A 30 × 40 cm painting with a 0.5 cm overlap has a 29 × 39 cm mat window. With a 5 cm border, the mat and glass are 39 × 49 cm. With 2.5 cm moulding, the frame is 44 × 54 cm on the outside, and you need about 1.96 m of moulding.
Good to know
- The moulding width here is the full width of the frame profile. The part that sits over the glass (the rebate) is already inside this width.
- Framers add a little clearance so the glass is not a tight fit. Ask your framer, especially for large pieces.
- Works on paper and textiles are often framed with acid-free mats and backing to protect them over time.
Frequently asked questions
How wide should a mat border be?
There is no single rule. Wider borders give a small artwork more presence; many framers choose a border that looks balanced with the frame and the wall.
Why add extra mat at the bottom?
A slightly deeper bottom border, sometimes called bottom weighting, can stop the artwork looking as if it is sliding down. It is a matter of taste.
How much should the mat overlap the artwork?
Usually a few millimetres on each side, enough to hold the art in place. Check that the overlap does not hide a signature or important detail.