About the Picture Mat and Frame Calculator
This picture mat and frame calculator does the arithmetic of framing for you. Enter the size of your print or artwork, how much the mat should overlap it, and either the border width you want or the frame you already own. It returns the mat window opening to cut, the outer mat size (which is also the frame’s rabbet or opening size), the border on every side, the finished outside size of the frame and the length of moulding to buy.
It suits photographers matting prints for exhibitions, artists preparing work for sale, and DIY framers cutting their own mats and mitred frames. Two common habits are built in: the window is cut slightly smaller than the art so the mat hides its edges, and the bottom border can be weighted a little wider than the top and sides, which looks optically centred on a wall.
Work in inches or centimetres — all values use the unit you choose. The calculator also suggests the smallest standard ready-made frame that will hold your matted piece, so you can decide between an off-the-shelf frame and a custom one.
How to use the picture mat and frame calculator
- 1Pick inches or centimetres and enter the artwork’s width and height.
- 2Set how far the mat should overlap each edge of the art.
- 3Choose whether you want a set border width or need to fit an existing frame.
- 4Add bottom weighting and the moulding face width if you are building the frame.
- 5Use the cut list to cut the mat window and buy the right length of moulding.
Formula and method
The mat window is the artwork size minus the overlap on both sides, so the mat hides a small strip around the edge and holds the art flat. In border mode, the outer mat size is the window plus the border b on each side, with an extra e added to the bottom for a weighted mat. In frame mode the outer mat equals the frame opening, and the borders are what is left: side = (frame W − window W) ÷ 2 and top = (frame H − window H − e) ÷ 2.
Mitred moulding is measured along its outside edge, so each side is the opening plus two moulding widths. Adding all four sides gives 2 × (mat W + mat H) + 8 × the moulding face width; a waste allowance covers saw kerf, the mitre offcuts and any defects. Frame opening (rabbet) clearance of about 1/16 in is usually built into the frame, so it is not added here.
- b
- Border width at the top and sides
- e
- Extra width added to the bottom border
- m
- Moulding face width
Worked examples
8 × 10 in print with 2.5 in borders
The window is 8 − 0.25 = 7.75 in by 9.75 in. Adding 2.5 in borders, plus 0.5 in extra at the bottom, gives a 12.75 × 15.25 in mat. Moulding needs 2 × 28 + 8 = 64 in, or 70.4 in (about 5.9 ft) with 10% waste. The nearest ready-made frame it fits is 14 × 18 in.
11 × 14 in photo in a 16 × 20 in frame
The window is 10.75 × 13.75 in. Across the width, (16 − 10.75) ÷ 2 = 2.625 in per side. Vertically, (20 − 13.75 − 0.5) ÷ 2 = 2.875 in at the top and 3.375 in at the bottom.
30 × 40 cm print, 6 cm borders, 3 cm moulding
A 0.5 cm overlap gives a 29 × 39 cm window. With 6 cm borders and 1 cm extra at the bottom the mat is 41 × 52 cm. Moulding: 2 × 93 + 24 = 210 cm, or 231 cm with 10% waste. An A2 (42 × 59.4 cm) frame is the smallest standard size that holds it.
Frequently asked questions
How much smaller should the mat opening be than the picture?+
Cut the window about 1/4 in (roughly 0.5–1 cm) smaller than the art in each dimension — an overlap of 1/8 in on each side. That hides the edges and stops the art falling through. For floated or deckle-edged art, cut the window larger instead.
What is a good mat border width?+
Common borders are 2–3 in (5–8 cm) for prints up to about 11 × 14 in and 3–4 in for larger work. Wider borders give a gallery look; borders much narrower than the frame moulding tend to look cramped.
Why is the bottom border of a mat wider?+
A slightly wider bottom border, called bottom weighting, makes the art look visually centred when hung at eye level. An extra 1/4–1/2 in (about 1 cm) is typical; equal borders are perfectly acceptable for a modern look.
How do I calculate how much frame moulding I need?+
Add the four sides of the frame opening and eight times the moulding width to account for the mitred corners, then add 10–15% for waste. For a 16 × 20 in opening with 1 in moulding that is 72 + 8 = 80 in before waste.
Is the outer mat size the same as the frame size?+
Yes. A frame sold as 16 × 20 in has a 16 × 20 in opening (rabbet) that holds a 16 × 20 in mat, glass and backing. The outside of the frame is larger by twice the moulding width.