Picture frame sizes are named after the print that fits behind the glass, not after the outside edge of the moulding. A frame sold as 16×20 in holds a 16×20 in print with no mat, or a smaller print with a mat. This chart lists the standard frame sizes in inches, centimetres and ISO A, says what fits each one, and shows how to measure.
Picture frame sizes chart: US frames in inches and centimetres
US frames follow the same inch sizes as US prints. The shape column tells you which other sizes share the same proportions. Our art print size guide shows how each size looks on a wall.
| Frame size (inches) | Centimetres | Shape |
|---|---|---|
| 5×7 in | 12.7×17.8 cm | 5:7 |
| 8×10 in | 20.3×25.4 cm | 4:5 |
| 11×14 in | 27.9×35.6 cm | 11:14 |
| 12×16 in | 30.5×40.6 cm | 3:4 |
| 12×18 in | 30.5×45.7 cm | 2:3 |
| 16×20 in | 40.6×50.8 cm | 4:5 |
| 18×24 in | 45.7×61 cm | 3:4 |
| 20×30 in | 50.8×76.2 cm | 2:3 |
| 24×36 in | 61×91.4 cm | 2:3 |
ISO and European picture frame sizes in centimetres
Outside North America, frames are sold as ISO A sizes or round centimetre sizes. Each A size is half the area of the one above it and all share the ratio 1:√2, about 1:1.414, as our guide to A1, A2 and A3 explains.
| Frame size (cm) | Inches | Shape |
|---|---|---|
| A4 (21×29.7 cm) | 8.3×11.7 in | ISO A |
| A3 (29.7×42 cm) | 11.7×16.5 in | ISO A |
| A2 (42×59.4 cm) | 16.5×23.4 in | ISO A |
| A1 (59.4×84.1 cm) | 23.4×33.1 in | ISO A |
| 13×18 cm | 5.1×7.1 in | about 5:7 |
| 20×25 cm | 7.9×9.8 in | 4:5 |
| 30×40 cm | 11.8×15.7 in | 3:4 |
| 40×50 cm | 15.7×19.7 in | 4:5 |
| 50×70 cm | 19.7×27.6 in | 5:7 |
| 60×90 cm | 23.6×35.4 in | 2:3 |
| 70×100 cm | 27.6×39.4 in | 7:10 |
What print fits each frame: with no mat and with a mat
With no mat, the print and the frame are the same size and the same shape. An A3 print goes in an A3 frame, and an 18×24 in print goes in an 18×24 in frame.
A mat is a card border between the print and the frame. It lets a smaller print sit in a larger frame, and it keeps the print off the glass. With a mat, the frame is usually one standard step up from the print. The mat opening is cut slightly smaller than the print, so the edges of the print stay hidden behind it.
| Frame with a mat | Frame in both units | |
|---|---|---|
| 8×10 in | 11×14 in | 11×14 in = 27.9×35.6 cm |
| 11×14 in | 16×20 in | 16×20 in = 40.6×50.8 cm |
| 16×20 in | 20×24 in | 20×24 in = 50.8×61 cm |
| A4 | A3 | 29.7×42 cm = 11.7×16.5 in |
| A3 | A2 | 42×59.4 cm = 16.5×23.4 in |
| 30×40 cm | 40×50 cm | 40×50 cm = 15.7×19.7 in |
| 40×50 cm | 50×70 cm | 50×70 cm = 19.7×27.6 in |
Whether you need a mat at all is covered in our guide to framing a poster with a mat, or without one.
Why the shape must match
A print only fits a frame of the same shape without cropping or a mat. The shapes in common use are 2:3, 3:4, 4:5, 5:7 and the ISO A ratio. Two near misses show how it goes wrong.
- A3 in a 30×40 cm frame. A3 is 29.7×42 cm and the frame is 30×40 cm, so the print is 2 cm taller than the frame. It does not fit. Buy an A3 frame.
- 24×36 in in a 60×90 cm frame. Both are 2:3, but the print is 61×91.4 cm. It is 1 cm wider and 1.4 cm taller than the frame, so it will not sit flat.
When the frame is the right shape but a step too large, a mat closes the gap evenly. When the shape is wrong, the mat borders come out uneven, wider at the sides than at the top, or the other way round.
Frame sizes that look alike but are not
Several US and centimetre frame sizes share a shape and differ by only a few millimetres: 8×10 in (20.3×25.4 cm) and 20×25 cm, 16×20 in (40.6×50.8 cm) and 40×50 cm, 18×24 in (45.7×61 cm) and 45×60 cm. In each pair the inch size is between 3 and 10 mm larger, which is enough to stop a print sitting flat. Buy the frame in the unit the print was made in.
A4 and US Letter show the same trap with different shapes. A4 is 8.3×11.7 in and Letter is 8.5×11 in, so A4 is slightly narrower and 0.7 in taller.
How to measure for a frame
- Measure the print itself, width first and then height, to the nearest millimetre.
- Divide the long side by the short side to find the shape: 1.5 is 2:3, 1.33 is 3:4, 1.25 is 4:5, 1.4 is 5:7 and 1.414 is an ISO A size.
- For a frame with no mat, match the frame size to the print size. For a mat, go up one standard step.
- Use the unit the frame is sold in. An 18×24 in print is 45.7×61 cm, not 45×60 cm, so a frame sold in inches is the safer match.
- Check the wall against the outside size of the frame. The outside is larger than the stated size by the width of the moulding on every side.
Frames and files at Montclair
Montclair prints come framed or unframed. Frames are available in black, white, natural wood or dark wood and arrive ready to hang. Unframed prints ship rolled in a protective tube, and shipping is free and tracked worldwide.
If you would rather buy a frame locally, most prints also come as an $8 Print Ready Package: seven print-ready files covering 4×6 in to 24×36 in and A4 to A1, a guide to printing them, and a personal-use licence. You can match the file to a frame you have already measured. Browse the black and white prints, or open a print such as Bugatti Type 35 Profile, and pick a size on the product page.
Common questions
What size frame do I need for an 8×10 print with a mat?
An 11×14 in frame (27.9×35.6 cm). The mat opening is cut slightly smaller than the 8×10 print so that it holds the edges.
Does an A4 print fit an 8.5×11 in frame?
Not without cropping. A4 is 8.3×11.7 in, so it is 0.7 in taller than an 8.5×11 in frame. Use an A4 frame, or an A3 frame with a mat.
What frame do I need for a 16×20 print?
A 16×20 in frame (40.6×50.8 cm) with no mat, or a 20×24 in frame (50.8×61 cm) with a mat.
Is the frame size the same as its outside size?
No. The frame size is the print it holds. The outside size adds the moulding on every side, so check the wall against the outside measurement on the listing.
