The short answer
A frame's size is the size of the picture it holds, its opening, not the outside of the frame: a 16 × 20 frame takes a 16 × 20 in print or mat and measures more across. A mat adds 2 to 4 in on each side and lets a print of any shape fit a ready-made frame, so an 11 × 14 in print sits neatly in a 16 × 20 frame.
Frame sizes confuse almost everyone the first time, because the size on the label is not the size of the frame. Once you know what each number measures, buying a ready-made frame for any print becomes easy.
Three measurements
A framed print has three sizes, nested one inside the other.
The print. The paper, for example 11 × 14 in.
The frame size. The size of the opening at the back of the frame, the space the glass, mat and print fill. A “16 × 20 frame” holds a 16 × 20 in piece of glass and a 16 × 20 in mat. This is the number on every label.
The outside size. The frame size plus the molding on every side. A 16 × 20 frame with a 1¼ in molding measures 18½ × 22½ in on the wall. Use the outside size when you plan a wall or a gallery group.
Standard US frame sizes
Ready-made frames come in a familiar set of sizes, each matching a common print or photo size:
- 5 × 7 and 8 × 10 for photographs and small prints on a desk or shelf
- 11 × 14 for small prints, often with an 8 × 10 print matted inside
- 16 × 20 for medium prints, or an 11 × 14 print with a mat
- 18 × 24 for posters and medium prints, or a 12 × 16 print with a mat
- 24 × 36 for large posters and prints, the usual size above a loveseat or as a pair above a sofa
There are many in between (12 × 16, 20 × 24, 24 × 30, 30 × 40), and every painting page here lists, for each print size, the frame it needs with no mat, a 2 in mat and a 3 in mat, and whether that frame is a ready-made size. Look for the print table on any painting page, such as Wheat Field with Cypresses.
What a mat does
A mat is the card border between the print and the frame. It adds 2 to 4 in (5 to 10 cm) on each side, keeps the print off the glass, and gives the picture breathing room, which makes almost any print look more expensive. It also solves the problem of proportions. Famous paintings come in every shape; frames come in a few. A mat window can be cut to any size, so the print fits the window and the mat fits the frame.
The mat window is cut about ¼ in smaller than the print on every side, so the mat holds the edges down. An 11 × 14 in print gets a 10½ × 13½ in window, and the mat’s outside edge is the frame size, 16 × 20. The border then comes to 2¾ in at the sides and 3¼ in at the top and bottom. Some framers make the bottom border a little deeper than the top, a traditional touch that keeps the picture from looking as if it is sliding down.
Ready-made or custom
Ready-made frames in standard sizes are inexpensive and quick, and with a custom-cut mat they suit almost any print. Custom framing makes sense for unusual sizes, very large pieces, conservation materials or a molding you love. A good compromise is a ready-made frame with a mat cut to order.
Floating frames for canvas
A canvas print on stretcher bars is usually hung unframed or in a floating frame: a shallow tray that sits around the canvas with a small gap, so the canvas appears to float. It needs no glass and no mat. Measure the canvas, and buy the floating frame for that size.
Glazing
- Glass is clear and scratch-resistant, and the usual choice for small and medium frames.
- Acrylic is lighter and shatter-resistant: the safe choice above a bed, in kitchens, bathrooms and children’s rooms, and for anything large.
- UV-filtering glass or acrylic slows fading in a sunny room.
- Anti-reflective glazing all but disappears, and is worth it opposite a window.
Metric A sizes
European A sizes have their own proportion (about 1 : 1.41) that no US frame matches exactly. A4 (8.3 × 11.7 in) is close to US letter, 8½ × 11; A3 (11.7 × 16.5 in) is close to 11 × 17; A2 (16.5 × 23.4 in) and A1 (23.4 × 33.1 in) fit 18 × 24 and 24 × 36 frames only with a mat. Print at a US size if you plan to buy a US frame.
The printing guide covers paper and resolution, and the art size calculator includes the frame and mat in every width it suggests.
Questions people ask
Can I put a famous painting's odd proportions in a standard frame?
Yes, with a mat. Print the painting whole at a size a little smaller than a standard mat window, then have a mat cut to that window inside a standard frame. The mat absorbs the difference, and nobody sees it.
Glass or acrylic?
Glass is clearer and harder to scratch. Acrylic is lighter and does not shatter, so it is the better choice above a bed, in a child's room, in a kitchen or bathroom and for large frames. Both come in anti-reflective and UV-filtering versions.
Do prints of museum paintings need UV-filtering glass?
In a sunny room, yes. Sunlight fades inks and yellows paper over the years, and UV-filtering glazing slows that down. In a dim hallway ordinary glazing is fine, and pigment inks on good paper fade far more slowly than dye inks.
Updated October 16, 2026. These are rules of thumb that designers start from; your room has the final say.