◆ In short
AI images are made for screens, and when they reach our counter they nearly always have two problems. The first and most common: proportions. AI works in square, 2:3 or 16:9, while posters (A2, A1, A0, 50×70, 70×100) all sit around 1:1.41: either you crop, or a white border remains. The fix is to ask the AI for the right format before generating. The second: pixels. A standard ChatGPT image is 1,536 pixels long, good for about 39 cm of print; an A1 needs at least 3,300. If the image is clean we upscale it ourselves; if it is already mushy, regenerate it larger. Paper: matt coated 120 gsm (A2 € 7, A1 € 13, A0 € 20).
Why an image that looks great on your phone is not enough for a wall
On a phone an AI-generated image looks perfect: the screen is small, bright and extremely pixel-dense. Printed at 84 cm it is a different story, because every pixel has to cover a much larger patch of paper.
As of October 2026 the most popular generators output, by default:
| Generator | Long side, by default | Notes |
|---|---|---|
| ChatGPT | 1,024–1,536 px | Classic sizes are 1024×1024, 1536×1024 and 1024×1536; newer versions can output larger |
| Gemini (Nano Banana) | about 1,000 px | The Pro version can reach 2K or 4K |
| Midjourney | about 1,000 px | The Upscale button doubles it: about 2,000 px |
These tools change often, so what matters is the file you actually have, not the table. To check it:
- Windows: right-click the file → Properties → Details → Dimensions
- Mac: open it in Preview → Tools → Show Inspector
- iPhone: open the picture in Photos and swipe up: the pixel size is listed underneath
The number to look at is the long side. With it, the table in the pixels section tells you how far you can go.
The problem we see most often: proportions
At the counter the most common trouble is not pixels but shape. AI thinks in screen and social-media proportions: square, 2:3, 4:5, 16:9. Posters, on the other hand, all have roughly the same shape: A2, A1 and A0 are 1:1.41, and 50×70 (1:1.4) and 70×100 (1:1.43) are very close to it.
When the two shapes do not match there are two ways out: crop part of the image, or leave a white border. Here is how much you lose on a portrait A1 (59.4 × 84.1 cm) when filling it edge to edge:
| AI proportion | What happens on an A1 |
|---|---|
| 3:4 | About 4 cm cropped from the width (6%): nearly always fine |
| 2:3 | About 5 cm cropped from the height (6%): nearly always fine |
| 4:5 | About 8 cm cropped from the width (12%): noticeable if something sits near the edge |
| 9:16 (stories, phone wallpapers) | Over 21 cm cropped from the height (20%) |
| 1:1 square | Almost a third of the width cropped, or about 25 cm of white left over |
Cropping hurts most when the subject runs right to the edge: a head, a line of text, a signature at the bottom. We look at the file before printing: if the proportions do not match we tell you, and we decide together whether to crop or keep a border.
The fix: ask for the right format before you generate
Say it in the prompt
ChatGPT and GeminiAdd the final format to your request, in a printer's words: "portrait image in A1 proportions, i.e. 1:1.41, to be printed as a poster".
If the tool only offers a few proportions, pick 3:4 or 2:3: they are the closest to the sheet and you lose only 6%. Remember to say portrait or landscape too: ask for "a poster", get a wide image, and you end up cropping half the scene.
Use the parameter
MidjourneyMidjourney takes the proportion as a parameter at the end of the prompt. For our posters:
--ar 5:7→ portrait, fits A2, A1, A0 and 50×70--ar 7:5→ the same, landscape
That way the image is born in the shape of the sheet and nothing gets cropped.
Have the image extended
If you have already made itIf you like the image as it is and do not want to regenerate it, ask the AI to extend the scene instead of cropping it: "extend the background at the top and bottom to a 1:1.41 ratio without changing the subject". Midjourney's Zoom Out and Pan commands do the same thing.
Check the added parts carefully: that is where AI most easily invents odd details.
Or keep the border
When you want to lose nothingA white border is not necessarily a compromise. Around a square image the margin works like a mount, and if the poster is going into a frame it is often the most elegant solution.
Just tell us: we centre the image on the sheet and keep the white even on both sides.
How many pixels each format needs
A poster is viewed from a metre or more, so you do not need the 300 dpi of a business card: 100 dpi at final size is the minimum for a good result, and 150 dpi keeps it sharp even up close. In pixels on the long side:
| Format | Minimum (100 dpi) | Sharp up close (150 dpi) |
|---|---|---|
| A2 · 42 × 59.4 cm | 2,350 px | 3,500 px |
| 50 × 70 cm | 2,750 px | 4,150 px |
| A1 · 59.4 × 84.1 cm | 3,300 px | 5,000 px |
| 70 × 100 cm | 3,950 px | 5,900 px |
| A0 · 84.1 × 118.9 cm | 4,700 px | 7,000 px |
The other way round, this is how far an image goes straight out of the AI, at 100 dpi:
- 1,024 px → about 26 cm on the long side
- 1,536 px → about 39 cm, smaller than A3
- 2,048 px → about 52 cm
- 3,840 px (4K) → about 97 cm, enough for an A1 and nearly for 70×100
In practice almost no image generated at default settings is enough for an A1: it needs enlarging. Not a disaster, but it has to be done properly.
Enlarging it: when we do it and when to regenerate
We upscale it
- ✓The image is clean: crisp edges, no mushy areas
- ✓It is the original file downloaded from the generator, not a copy
- ✓The proportions are already right, or nearly
- –Upscaling does not invent detail that is not in the file
Best for
A sharp image that just needs to get bigger. Send it as it is.
Better to regenerate it
- ✓The final result is sharper than any enlargement
- ✓It is the chance to fix the proportions too
- –The file is already grainy, compressed or full of glitches
- –Enlarging a flaw only makes it bigger
Best for
A damaged or tiny file. Remake it at the highest resolution the tool offers (Upscale on Midjourney, 2K or 4K where available) and send it again.
The mistakes that ruin the file before it reaches us
The screenshot
A screenshot of the image has the resolution of your screen, not the image's, and often drags bits of the interface along. Always download the file with the generator's download button.
WhatsApp as a photo
Sent as a photo, WhatsApp compresses and shrinks the image. Attach it as a document (or by e-mail, or upload it to the shop): it arrives identical to the original.
The flaws you cannot see on a phone
An extra finger, a wonky letter, mismatched earrings: invisible on a phone, the size of a hand on an A1. Before sending it, zoom to 100% on screen and inspect it piece by piece, especially hands, lettering and edges.
Which paper to print it on
For AI images we nearly always recommend matt coated 120 gsm paper: the classic poster and bill paper, good with colour, no glare from room lights, and inexpensive.
| Format | Matt coated 120 gsm | 200 gsm paper |
|---|---|---|
| A2 | € 7 | € 9 |
| 50 × 70 cm | € 8 | € 10 |
| A1 | € 13 | € 19 |
| 70 × 100 cm | € 15 | € 20 |
| A0 | € 20 | € 27 |
200 gsm makes sense if the poster will hang for years or go into a frame: it is stiffer and sits flat on the wall. For 50×70 and 70×100 there is also glossy photo 250 gsm (€ 20 and € 40), with deeper blacks but glare: avoid it under a spotlight or facing a window. All the differences are in the poster paper guide.
One thing to know about colour. A screen emits light; paper reflects it. The neon colours, glows and fluorescent skies AI loves come out a little duller on paper, and very dark images tend to close up in the shadows. It is not a printing fault: it happens on any printer. If the image is almost entirely dark, ask the AI for a slightly brighter version.
How to order it
- Online: upload the file at shop.guug.it/poster, choose size and paper, and it is ready within 24 hours.
- In store: bring the file (on a USB stick, by e-mail or as a document on WhatsApp). A poster takes about 30 minutes to print, plus whatever jobs are ahead of yours, and you can wait for it here, a short walk from St Peter's.
Either way we look at the file before printing: if the proportions do not match or there are too few pixels, we tell you before, not after. You can price any size instantly on the custom posters page.
Frequently asked questions
Can I print a ChatGPT image as an A1 poster?
Yes, but it nearly always needs enlarging. A standard ChatGPT image is 1,536 pixels long, enough for about 39 cm; an A1 needs at least 3,300. If the image is clean we upscale it before printing. Check the proportions too: a 2:3 image loses about 6% on an A1, a square one almost a third.
How many pixels do I need to print a poster?
On the long side, at least 2,350 px for an A2, 3,300 px for an A1 and 4,700 px for an A0: that is 100 dpi at final size, enough for a poster viewed from a metre. For a result that stays sharp up close you need 3,500, 5,000 and 7,000 px.
Why does my AI image get cropped when printed?
Because generators work in screen proportions (1:1, 2:3, 16:9) while A2, A1 and A0 sheets are 1:1.41. To fill the sheet part of the image falls outside, or a white border is left. To avoid it, ask the AI for a 1:1.41 ratio before generating, or use --ar 5:7 in Midjourney.
Do you upscale images that are too small?
Yes, if the image is good quality: crisp edges and the original file, not a screenshot or a picture sent through WhatsApp. If it is already grainy or full of glitches, enlarging it would only make them bigger: in that case regenerate it at the highest resolution available and send it again.
Which paper is best for an AI-generated image?
In most cases matt coated 120 gsm, the classic poster paper: A2 € 7, A1 € 13, A0 € 20. If the poster will hang for years or go into a frame, 200 gsm is better (A1 € 19, A0 € 27).
Why are the printed colours less vivid than on screen?
Because a screen emits light and paper reflects it. The neon colours and glows typical of AI images come out a little duller on paper, and very dark images close up in the shadows. It happens on any printer: if the image is almost entirely dark, ask the AI for a brighter version.
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