How to upscale an image for large-format printing
A 12-megapixel phone photo prints well at 30 × 40 cm, but a two-metre banner needs 5 to 20 times more pixels. This guide explains how many you need, which resolution is enough depending on where it is seen from, and how to get there with AI upscaling without inventing what was never there.
How many pixels you need: the ppi rule
Printers think in pixels per inch (ppi). To work out the pixels one side needs: centimetres ÷ 2.54 × ppi. A 60 × 40 cm canvas at 150 ppi needs 3543 × 2362 pixels (8.4 MP). A 200 × 100 cm banner at 100 ppi, 7874 × 3937 (31 MP). A 400 × 300 cm vinyl at 50 ppi, 7874 × 5906 (46 MP).
| Medium | Usual distance | ppi that are enough | Example |
|---|---|---|---|
| Print in hand, magazine, catalogue | 30 cm | 300 | 20 × 30 cm → 2362 × 3543 px |
| Canvas or poster on a wall | 1 m | 150 | 60 × 90 cm → 3543 × 5315 px |
| Roll-up, shop sign | 2 m | 100 | 85 × 200 cm → 3346 × 7874 px |
| Banner, billboard, window vinyl | 5 m or more | 30 to 60 | 300 × 200 cm → 4724 × 3150 px at 40 ppi |
Distance matters more than size: the eye cannot resolve pixels below about 0.3 mm at one metre. That is why billboards are printed at 20 ppi and look perfect from the pavement.
What happens when you upscale without AI
Photoshop, Gimp or the print shop can stretch the image (bicubic interpolation). It adds no information: each original pixel is spread over several and the result looks soft, with stepped edges on text and lines. It works up to 130–150 % of the original size; beyond that the missing detail shows even from a distance.
What AI upscaling does and does not do
A super-resolution model such as Real-ESRGAN has seen millions of small/large image pairs and learns what fine detail usually looks like: fabric weave, stone grain, the edge of a letter. When upscaling it rebuilds that detail consistently with what is there, which is why a ×4 upscale looks sharp where bicubic looks blurry. What it cannot do is read illegible text or recover a face that cannot be made out: it rebuilds plausible detail, not lost information. On Airpic, ×2 and ×4 take seconds; ×8, ×16 and the up-to-600-megapixel mode process in 250-tile mosaics.
Step by step on Airpic
- Upload the original at the best quality you have (the phone or camera JPEG, not a WhatsApp copy).
- Choose For large-format printing and type the print size in centimetres. Airpic calculates the ppi you will get at each factor and tells you whether it is enough for that distance.
- Pick ×2, ×4, ×8, ×16 or Max (up to 600 MP). For photos, the “sharp” style; for illustrations and soft textures, “painterly”.
- If there are people, enable enhance faces.
- Check the result in the comparator (free) and download the full file as PNG, JPEG or WebP.
Hand the file to the printer in the colour space they ask for; Airpic keeps the input ICC profile.
Common mistakes
- Upscaling an image that was already upscaled or compressed several times: each pass invents on top of inventions. Always go back to the original.
- Asking for 300 ppi on a banner: it multiplies the file size by ten with no visible difference at three metres.
- Forgetting bleed: add 3–5 mm per side before upscaling if the printer requires it.
- Saving a print file as a heavily compressed JPEG: use quality 92 or higher, or PNG.
FAQ
How many megapixels do I need to print a 2 × 1 metre banner?
At 100 ppi, 7874 × 3937 pixels (31 MP). At 60 ppi, which is enough when viewed from more than two metres, 4724 × 2362 (11 MP) will do.
Can an image be upscaled 400 % without losing quality?
With classic interpolation, no: it looks blurry. With AI super-resolution you do get a sharp, consistent image, as long as the original has some detail to rebuild.
What resolution does an image need for an A3 print?
A3 is 29.7 × 42 cm. At 300 ppi, 3508 × 4961 pixels (17 MP); at 200 ppi, which already looks perfect on a wall, 2339 × 3307 (7.7 MP).
How much does upscaling for print cost on Airpic?
Up to 32 output megapixels counts as a standard image (from €0.099). Above that, as large format (from €0.49 in the 100 pack). Previewing the result is always free.