Size guide
What size frame for an A3 print?
An A3 print fits an A3 frame exactly; in the US, the practical ready-made answer is usually a 16×20 frame with a mat. A3 frames are ordinary in the UK, EU and Australia, but true A3 is rare on US store shelves, so the mat often does the translation.
Quick answer
Buy A3 where metric frames are stocked; in the US, mat A3 into 16×20
| Frame | Mat opening | Even border (sides · t/b) | Bottom-weighted (t · b) | Glass / backing |
|---|---|---|---|---|
| A3 — snug, no mat 29.7 × 42.0 cm | — | — | — | 11 9/16 × 16 7/16″ |
| 16×20 40.6 × 50.8 cm | 11 3/16 × 16 1/16″ | 2 3/8 · 2″ | 1 3/4 · 2 1/4″ | 15 7/8 × 19 7/8″ |
| A2 42.0 × 59.4 cm | 11 3/16 × 16 1/16″ | 2 11/16 · 3 11/16″ | 3 7/16 · 3 15/16″ | 16 7/16 × 23 1/4″ |
| 18×24 45.7 × 61.0 cm | 11 3/16 × 16 1/16″ | 3 3/8 · 4″ | 3 3/4 · 4 1/4″ | 17 7/8 × 23 7/8″ |
A3 is normal in metric markets, awkward in US aisles
In London, Sydney or Berlin, the boring answer is often the best one: buy an A3 frame. In many US stores, the A-series rack is missing or thin, and the closest inch frame is not a snug fit. The mat, called a mount in UK/AU framing language, becomes the adapter between systems.
The important trap is 12×16. It sounds close, but true A3 is 16.54″ tall, so it overhangs a 12×16 frame. A 16×20 frame is larger than the print in both directions and gives enough room for a real mat instead of a squeezed edge.
Worked example: A3 print in a US 16×20 frame
A3 is 11.69 × 16.54″ before the mat overlap. With the standard ¼″ overlap, the opening rounds to 11 3/16 × 16 1/16″. Put that opening inside a 16×20 frame and the borders come out to about 2⅜″ on the sides and 2″ at the top and bottom.
That is a balanced enough border for a US ready-made frame. A bottom-weighted option moves the vertical split to about 1¾″ top and 2¼″ bottom. For an exact metric frame, use the frame size calculator; for a frame already in your cart, test it with the fit checker.
Takeaways for US buyers
If you can buy a real A3 frame, do that for a no-mat fit. If you are shopping US ready-made sizes, skip 12×16 for true A3 and use 16×20 with a mat. For the neighboring document size, see the A4 frame guide.
Common mistakes
- Reaching for 12×16. A3 is too tall for that frame, even though the numbers look nearby.
- Confusing A3 with tabloid. Tabloid is 11×17, while A3 is wider and slightly shorter. Their frames are not interchangeable.
- Expecting an inch-frame match. A-series paper uses a 1:1.41 ratio, so US frames need a mat unless the listing is actually A3.
Frequently asked questions
What is the A3 frame size in inches and cm?
A3 is 297 × 420 mm, or 29.7 × 42 cm. In inches it is about 11.69 × 16.54, which is why a true A3 print needs either an A3 frame or a larger matted frame.
What is the closest US frame to A3?
A 16×20 is the practical US choice for a matted A3 print. Do not use 12×16 for true A3; A3 is 16.54 inches tall, so it is taller than that frame.
Can an A3 print go in a 16×20 frame?
Yes. The mat window is about 11 3/16 × 16 1/16 inches, leaving 2⅜ inch side borders and 2 inches at the top and bottom inside a 16×20 frame.
Is A3 two A4 sheets?
Yes. Two A4 sheets side by side make A3, and the shared A-series ratio is why A3 frames are easy to stock in metric countries but awkward in US inch sizes.
What size mat for an A3 in an 18×24?
Use an opening about 11 3/16 × 16 1/16 inches. In an 18×24 frame, that leaves roughly 3⅜ inch side borders and 4 inches at the top and bottom.