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Standard frame and print sizes
A4 and 21 × 30 are not the same thing. An 8 × 10" fits no European frame. Here are all the sizes, with the mat maths and the final hanging measurement — the one nobody publishes.
ISO sizes: A4, A3, A2, A1
ISO 216 is the European system and the one nearly every print-on-demand house uses. It has one very practical property: each size is exactly half the one above it, cut along the long side. An A3 is two A4s; an A2 is two A3s.
| Format | Millimetres | Inches | What it's for |
|---|---|---|---|
| A6 | 105 × 148 | 4.1 × 5.8 | Postcards, mini prints |
| A5 | 148 × 210 | 5.8 × 8.3 | Small clusters, bedside |
| A4 | 210 × 297 | 8.3 × 11.7 | The best-selling print size |
| A3 | 297 × 420 | 11.7 × 16.5 | Single piece on a small wall |
| A2 | 420 × 594 | 16.5 × 23.4 | Anchor piece in a set |
| A1 | 594 × 841 | 23.4 × 33.1 | Single piece over furniture |
| A0 | 841 × 1189 | 33.1 × 46.8 | Poster format, large wall |
Careful with A4 and "21 × 30". They aren't the same: A4 is 210 × 297 mm and the commercial 21 × 30 format is 210 × 300 mm exactly. Three millimetres — but in a tight frame, three millimetres is the difference between fitting and not.
The round centimetre sizes
Alongside ISO you'll find round metric sizes, which is what most frame shops stock. They share no common proportion, and that matters: a 30 × 40 print is not an enlargement of a 21 × 30, it's a different shape.
| Size | Ratio | Typical use |
|---|---|---|
| 13 × 18 cm | 1:1.38 | Tabletop |
| 21 × 30 cm | 1:1.43 | The commercial equivalent of A4 |
| 30 × 40 cm | 1:1.33 | The most stocked frame size |
| 40 × 50 cm | 1:1.25 | Nearly square; works with a wide mat |
| 50 × 70 cm | 1:1.40 | The living-room piece |
| 60 × 80 cm | 1:1.33 | Large statement piece |
| 70 × 100 cm | 1:1.43 | Poster format |
US sizes, in inches
The American market uses neither ISO nor round centimetres. If you sell there, these are the sizes your customer expects — and none of them matches a European one:
| Inches | Centimetres | Closest European size |
|---|---|---|
| 5 × 7" | 12.7 × 17.8 | 13 × 18 (near enough) |
| 8 × 10" | 20.3 × 25.4 | None: squarer than A4 |
| 11 × 14" | 27.9 × 35.6 | Between 30 × 40 and A3 |
| 16 × 20" | 40.6 × 50.8 | 40 × 50 (near enough) |
| 18 × 24" | 45.7 × 61 | None |
| 24 × 36" | 61 × 91.4 | 60 × 90 (near enough) |
An 8 × 10" doesn't fit any standard European frame, and an A4 doesn't fit any American one. If you sell both sides of the Atlantic, either double your size variants or pick one system and say so plainly on the product page.
The mat: the sum nobody does
The mat — the passepartout, the board around the artwork — sits outside the print, it doesn't cover it. That sounds obvious and it's the source of half the confusion: it means the finished frame is bigger than the print, not that the print looks smaller.
Mat per side = (frame size − print size) ÷ 2
A 30 × 40 print in a 40 × 50 frame leaves 5 cm of board on every side. If the frame is exactly the print's size, there's no mat at all: the work goes full-bleed.
Widths that get used in practice: 40 mm is standard and 70 mm is the wide version, which reads as gallery framing and works beautifully with a small work in a large frame. Below 30 mm the mat stops reading and looks like a cutting error.
Which frame for which print
Combinations that work, with the mat already worked out:
| Frame | Resulting mat | Final hanging size | |
|---|---|---|---|
| 21 × 30 | 21 × 30 | No mat | ≈ 24 × 33 with a 15 mm moulding |
| 21 × 30 | 30 × 40 | 4.5 × 5 cm | ≈ 33 × 43 |
| 30 × 40 | 40 × 50 | 5 × 5 cm | ≈ 43 × 53 |
| 40 × 50 | 50 × 70 | 5 × 10 cm | ≈ 53 × 73 |
| 50 × 70 | 70 × 100 | 10 × 15 cm | ≈ 73 × 103 |
Look at that last column, because it's the one that actually hangs on the wall and the one almost no store publishes. When a customer reads "50 × 70" and an object 73 × 103 arrives, that's thirty centimetres a side. That's where returns start.
If you sell online: publish the final size
- Give the mounted size, not just the paper. Even in brackets.
- Make size a variant, never a table. As a Shopify variant the customer picks it and sees price and size together; in a table inside the description, nobody reads it.
- Show the scale, not the number. "50 × 70 cm" means nothing to most people. Seeing it on their own wall does.
Let them see the size on their wall, not in a table
InRoom Wall Art draws your moulding in real millimetres, with its mat, on your customer's wall at true size. Free plan: three artworks, no card.
See it on the Shopify App Store →Keep reading: what size art goes above a sofa, or how to cut size-related returns.