Poster resolution: how many pixels a large print really needs

The rule nobody tells you: resolution depends on viewing distance

Every print shop quotes the same figure when you ask what resolution a poster needs: 300 dpi. The number is not wrong, it is incomplete. 300 pixels per inch is roughly what an eye with normal vision needs to stop seeing individual dots at a reading distance of about 30 cm, the distance at which you hold a brochure. Move the print further away and the eye's ability to separate fine detail drops in proportion. At one metre most people cannot tell 200 ppi from 300. At two metres, 150 ppi looks sharp. At ten metres, which is where you stand to look at a banner on the side of a building, 30 ppi is plenty, and that is why roadside billboards are printed at 20 to 30 ppi.

So the rule is this: the resolution a poster needs depends on how far away people will stand, not on the size of the paper. A large print is, by definition, looked at from further away, and that one fact rescues most of the photos a 300 dpi checklist would reject.

Working figures, by distance:

• In the hand (30 cm): 300 ppi. Flyers, brochures, anything people pick up.
• On a desk or a shelf (50 cm): 250 to 300 ppi.
• On a wall, close up (1 m): 200 ppi. A3 posters on a noticeboard.
• Poster in a room (2 m): 150 ppi prints well, and 120 ppi is still acceptable. A1 and A0 event posters.
• Across a hall (3 m): 100 ppi. Exhibition panels, stage backdrops.
• Banner or vinyl at 5 m or more: 60 ppi and below. At 10 m, 30 ppi.

On units: the file has pixels (ppi), the printer lays down dots (dpi). For sizing a print, treat them as the same number.

One honest reservation. The distance rule assumes people stand where they normally would. A print in a narrow corridor, a shop window people press up against, or a conference poster read for its small type all get looked at from arm's length, and for those 300 ppi is still the right target. Before you size anything, ask where the nearest viewer will stand, and size the file for that person.

The sums: A3, A1, A0 and a two-metre banner

The formula fits on one line: pixels = centimetres ÷ 2.54 × ppi. Divide each side of the print in centimetres by 2.54 to get inches, multiply by the ppi your viewing distance needs, and you have the pixels the file must have on that side. Multiply the two sides together and divide by a million for megapixels. The same formula in reverse tells you how big you can print what you already have: pixels ÷ ppi × 2.54 = centimetres.

Here it is applied to the sizes people actually order when they print a large poster:

• A3 (29.7 × 42 cm) on a noticeboard, read from about a metre, at 200 ppi: 29.7 ÷ 2.54 × 200 = 2339 px by 3307 px, about 7.7 MP. The 300 ppi version, 3508 × 4961 px (17.4 MP), is only needed if people will hold the sheet.
• A1 (59.4 × 84.1 cm), an event poster seen from two metres, at 150 ppi: 3508 × 4967 px, about 17.4 MP. Notice that this is the same pixel count as A3 at 300 ppi: four times the paper, the same pixels, because the viewer stepped back. At 300 ppi an A1 would need 7016 × 9933 px (70 MP), which no phone produces and no viewer at two metres would notice.
• A0 (84.1 × 118.9 cm), the question people type as how many megapixels to print A0: at 150 ppi, 4967 × 7022 px, about 35 MP. At 120 ppi, which is the floor for a poster seen from two metres, 3973 × 5617 px (22 MP).
• A 200 × 100 cm banner on a stand or a fence, seen from five metres, at 60 ppi: 4724 × 2362 px, about 11 MP. From ten metres at 30 ppi: 2362 × 1181 px, under 3 MP. The image for a banner almost never lacks pixels. What it lacks, as the next section explains, is cleanliness.

Now put a 12 MP phone photo (4032 × 3024 px) next to those figures. At 150 ppi it prints 68 × 51 cm, so an A2 poster (42 × 59.4 cm) seen from two metres is covered straight out of the phone. An A1 at 150 ppi needs 3508 px on the short side and the photo has 3024: just short, so ×2 (8064 × 6048 px) covers it and covers A0 as well. Only when a print shop insists on 300 dpi for an A0 (9933 × 14043 px, 140 MP) does the request stop making sense, and that is the moment to say the words viewing distance to them.

Two things the sums do not show. Aspect ratio: A-series paper is 1:1.414 and a phone photo is 4:3, so crop the photo to the poster's proportions before you do anything else, or plan for white borders; every pixel you upscale and then cut off is wasted time. Bleed: most printers want 3 to 5 mm of extra image on each edge, so add about 1 cm to each dimension before you run the formula.

Check the original before you upscale: noise, compression and focus

Upscaling multiplies whatever is in the file. A clean 3 MP photo becomes a clean 48 MP one at ×4; a noisy, over-compressed, slightly soft one becomes 48 MP of large, well-defined noise grains, large, well-defined JPEG blocks and a softness spanning four times as many pixels. The model does its best to tell detail from damage, but it is far better to remove the damage before it is enlarged sixteen times in area. Look at three things, in this order, at 100% on your screen.

Noise. Coloured speckle in the shadows and a grainy texture in flat areas, typical of phone photos taken at night or indoors at high ISO. Run the photo through the tool to remove noise from a photo first, at a moderate strength: the aim is to take out the speckle and keep the texture of skin, fabric and foliage, so start around the middle of the slider and compare at 100%. Too much denoising leaves plastic surfaces that the upscaler will then enlarge faithfully. Denoise first, upscale second: the other way round you are cleaning sixteen times as many pixels for a worse result.

Compression. Square blocks in smooth areas, halos around hard edges, banding in skies: the signature of a JPEG saved at low quality or saved many times, which describes most images from a website, a messaging app or a screenshot. The denoiser at a low strength also smooths block artefacts. The honest warning most guides skip: a 600 px wide image that has been through a chat app will never make an A1 you can read from a metre away. The upscaler gives crisp edges to blocks that were never in the scene, and crisp blocks look worse than soft ones. If your source is a pixelated WhatsApp photo, ask the sender for the original before you spend any time on it.

Focus. Decide whether the softness is motion blur (smeared in one direction, from a slow shutter) or defocus (evenly soft, points of light turned into discs). The tool to sharpen a blurry photo analyses the image, suggests which of the two it is and lets you set the strength. It corrects slight blur well. It cannot bring back a subject that is a smear, and upscaling a smear produces a bigger smear with sharper edges. If the face you care about is not recognisable at 100% on screen, no poster will make it so.

One thing you do not have to fix: Airpic applies the EXIF rotation on upload and keeps the ICC profile, so a HEIC, a 16-bit TIFF or an AVIF comes out the right way up and in the right colours.

Large-format mode: why tiles reach sizes a single pass cannot

A GPU upscales an image by holding it in memory, running it through the network and writing out the result, and memory is the ceiling. A single pass handles a normal photo up to ×4, which is how Airpic runs ×2 and ×4. Beyond that the numbers run away: a 12 MP phone photo is 192 MP at ×4 and would be 768 MP at ×8, more than one pass can hold and more than any print needs.

The large-format factors (×8, ×16 and Max) therefore work differently. Airpic cuts the image into a mosaic of roughly 250 tiles, upscales each tile with a margin that overlaps its neighbours, and blends the overlaps back together so that no seam is visible in the result. The output can reach 600 megapixels, which for a 3:2 image is a print of around 5 × 3.4 metres at 150 ppi. The input for those factors can be up to 37.5 MP; if your factor would push the output past 600 MP, Airpic says so before it starts and offers Max, which scales to the largest size under the limit.

Bigger is not better. The right factor is the smallest one that gives you the ppi your viewing distance needs. A larger factor costs more processing time and a heavier file, and the print shop's software will downsample it to the resolution of the press anyway. Airpic shows the output pixels before you start, so check them against the sums above rather than guessing.

The other decision in this mode is the Style, under Advanced settings:

• Extreme sharpness for photographs with fine texture (hair, fabric, foliage, brickwork), text and architecture: it rebuilds micro-detail and keeps edges hard.
• Painterly fill for illustrations, watercolours, soft gradients, out-of-focus backgrounds and portraits where the skin should stay smooth. It fills with continuous strokes instead of inventing grain that reads as grit when enlarged.

Flat drawings are a separate case: line art, logos and anime frames have hard outlines and solid colours that a photo model tends to blur or texture; for those, use the tool to upscale anime and illustrations.

A practical warning about judging the result. Extreme sharpness on a soft-focus portrait can make skin look like sandpaper at 100% on a monitor 50 cm from your face, and the same file looks perfect printed at A1 and seen from two metres, the only view that matters. Inspecting a large-format file at 100% on screen is the most common reason people reject a file that would have printed beautifully. Zoom out until the image on screen is about the size it will appear from the viewing distance, and judge it there.

Step by step: upscale an image for a poster or banner in Airpic

Here is the whole process in the upscale an image tool, for a poster that will hang in a room and for a vinyl banner seen from the street. No account, no subscription; processing and the preview are free.

1. Drop the photo in. JPG, PNG (with transparency and 16-bit), WebP, TIFF, HEIC and AVIF are all accepted, so an iPhone HEIC goes straight in. A card appears with the thumbnail, the file name and the input and output pixels; the output figure updates as you change the settings. Crop to the poster's proportions first if you have not yet.
2. Under Use, choose For large printing. Enter the print size in centimetres (width and height) or pick a preset such as A3, A2, A1, Canvas 60×90 or Banner 100×200. Then set the viewing distance: In hand (30 cm), Desk (50 cm), Wall, close up (1 m), Room (2 m), Poster (3 m) or Banner (5 m or more). Airpic shows the ppi each factor would give at that size with a verdict (excellent for large format, fine for large format, or tight: looks good only from afar), preselects the smallest factor that passes, and keeps your choice if you change it by hand.
3. Pick the scale. ×2, ×4, ×8, ×16 or Max (600 MP). For an A1 from a 12 MP phone photo seen at two metres, ×2 is enough and the verdict says so. For a 2 × 1 m banner from the same photo the original already passes at 60 ppi. Save ×8 and ×16 for small originals: a 1200 × 900 px image that has to become an A1 is a job for ×4 (4800 × 3600 px, about 145 ppi on the long side), with the focus checked first.
4. Open Advanced settings. Choose the Style: Extreme sharpness for photos and text, Painterly fill for illustration and soft subjects. Set the Output format to PNG for the printer: lossless, with the ICC profile embedded. If the print shop insists on JPG, choose it (saved at high quality); auto matches your original's format. Tick Enhance faces (AI) only for portraits where the face fills a good part of the frame: on faces under about 100 pixels in the original the reconstruction drifts towards a generic face, and Airpic warns you when that happens.
5. Press Process image and check the preview. The ×2 and ×4 passes are quick: in our test on 19 September 2026, a 320 × 240 px photo upscaled ×4 to 1280 × 960 px in 5 seconds, and on 3 September 2026, with photos between 0.3 and 1 megapixel, ×4 took between 6 and 9 seconds, or about 17 seconds with Enhance faces switched on. The mosaic factors take longer. When it is done, drag the before/after slider, use View at 100% to inspect a detail, then zoom out and judge it at the viewing distance.
6. Download and hand it to the printer. The first full download each month is free; after that the tool uses credits that do not expire, and the current cost is on the tool page. Send the printer the PNG with its embedded profile and let them convert it for their press (why is explained in RGB to CMYK: what really happens to your colours in print), and tell them the viewing distance you sized for, so nobody runs the 300 dpi checklist over your file. Your file is deleted one hour after you download it, one day at most, is processed on GPUs in the European Union, and is never used to train anything.

For the full tables and the calculator, read how to upscale an image for large-format printing. Otherwise, you have the sums, the checks and the settings: open upscale an image, type in the size and the distance, and let the verdict tell you which factor your poster really needs.

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