You have a photo you love and a wall that needs it at poster size. Two questions decide whether that works: does the photo have enough pixels for the size you want, and how do you get something that big printed? This guide answers both with real numbers, and the free Photo to Poster Maker does the sums and builds the print files in your browser.
How to enlarge a photo to poster size, step by step
- Start from the original file. A photo sent through WhatsApp or saved from social media has been shrunk, often to under 2 MP. Copy the original from your phone or camera.
- Pick the poster size in the Photo to Poster Maker: A0 to A4, US sizes such as 18 × 24 or 24 × 36 in, or a custom size. Choose Fill to crop the photo to the poster's shape (drag to choose the crop), or Fit to keep the whole photo with a white border.
- Read the print-quality meter. It divides your photo's pixels by the poster's inches: 200 DPI and up is excellent, 150–199 good, 100–149 fair for a poster viewed from across a room, and below 100 the print will look soft.
- Fix a low score by choosing a smaller size, or by upscaling a small photo with AI (more on that below).
- Download. Get one PDF of A4, US Letter or A3 pages for a home printer, or one large JPG or PNG for a print shop.
How big can I print my photo? (resolution chart)
Print size is pixels divided by DPI. The chart shows the largest print each common photo size makes without enlarging, rounded to the nearest centimetre:
| Photo | Pixels | At 300 DPI | At 150 DPI | At 100 DPI |
|---|---|---|---|---|
| 2 MP (old phone, WhatsApp-compressed photo) | 1,600 × 1,200 | 14 × 10 cm | 27 × 20 cm | 41 × 30 cm |
| 8 MP (older phone) | 3,264 × 2,448 | 28 × 21 cm | 55 × 41 cm | 83 × 62 cm |
| 12 MP (most phones today) | 4,000 × 3,000 | 34 × 25 cm | 68 × 51 cm | 102 × 76 cm |
| 24 MP (entry DSLR or mirrorless) | 6,000 × 4,000 | 51 × 34 cm | 102 × 68 cm | 152 × 102 cm |
| 48 MP (phone in full-resolution mode) | 8,000 × 6,000 | 68 × 51 cm | 135 × 102 cm | 203 × 152 cm |
So a 12 MP phone photo makes a sharp A2 (59.4 × 42 cm) at about 171 DPI. Pushed to 24 × 36 in, the same photo drops to 111 DPI: still acceptable on a wall seen from a few steps back, but soft up close. A0 would be 85 DPI, which is too low for most photos. The guide to DPI explains why the DPI number stored in a file doesn't change any of this; only pixels do.
Poster sizes chart (A0–A4 and US sizes)
The pixels each size needs. 150 DPI is the poster target; 300 DPI is the photo-print target.
| Size | cm | inches | Pixels at 150 DPI | Pixels at 300 DPI |
|---|---|---|---|---|
| A0 | 84.1 × 118.9 | 33.1 × 46.8 | 4,967 × 7,022 | 9,933 × 14,043 |
| A1 | 59.4 × 84.1 | 23.4 × 33.1 | 3,508 × 4,967 | 7,016 × 9,933 |
| A2 | 42 × 59.4 | 16.5 × 23.4 | 2,480 × 3,508 | 4,961 × 7,016 |
| A3 | 29.7 × 42 | 11.7 × 16.5 | 1,754 × 2,480 | 3,508 × 4,961 |
| A4 | 21 × 29.7 | 8.3 × 11.7 | 1,240 × 1,754 | 2,480 × 3,508 |
| 11×17 in | 27.9 × 43.2 | 11 × 17 | 1,650 × 2,550 | 3,300 × 5,100 |
| 18×24 in | 45.7 × 61 | 18 × 24 | 2,700 × 3,600 | 5,400 × 7,200 |
| 24×36 in | 61 × 91.4 | 24 × 36 | 3,600 × 5,400 | 7,200 × 10,800 |
| 27×40 in | 68.6 × 101.6 | 27 × 40 | 4,050 × 6,000 | 8,100 × 12,000 |
27 × 40 in is the standard one-sheet movie poster; 18 × 24 and 24 × 36 in are the common US frame sizes. If your photo's shape doesn't match the poster's (a 4:3 phone photo on a 1:1.41 A-size sheet, for example), something has to give: either a little of the photo is cropped, or a white border is left.
How to print a poster at home on A4 paper
Any printer can make a poster if the poster is split into pages. The table shows how many sheets each size needs with a 6 mm printer margin and 5 mm of overlap for gluing, with the paper turned whichever way uses fewer sheets:
| Poster | A4 sheets | US Letter sheets |
|---|---|---|
| A3 | 4 (2 × 2) | 4 (2 × 2) |
| A2 | 8 (2 × 4) | 6 (2 × 3) |
| A1 | 12 (4 × 3) | 12 (3 × 4) |
| A0 | 21 (3 × 7) | 24 (4 × 6) |
| 18×24 in | 8 (2 × 4) | 8 (2 × 4) |
| 24×36 in | 15 (3 × 5) | 15 (3 × 5) |
- Print at 100% / Actual size. “Fit to page” shrinks each sheet by a few percent and the seams will not line up. The first page of the PDF has a 10 cm line: measure it before printing the rest.
- Lay the sheets out using the assembly guide. Rows are letters and columns are numbers, so A1 is the top left.
- Trim and overlap. Cut the white margin off the top and left of each sheet along the corner marks, then lay it over its neighbour so the cut edge meets the dashed line. The overlap hides small cutting errors; a craft knife and a metal ruler give straighter edges than scissors.
- Join from the back with tape or a glue stick, one row at a time, then trim the outside edge.
Thicker paper (120–160 g/m²) cockles less under heavy ink than standard 80 g/m² copy paper, and matte paper hides the seams better than glossy.
Print at home vs print shop: which is better?
- At home is fastest and nearly free if you have ink, and any size is possible. The seams show if you look closely, and colour can shift slightly between sheets as ink runs low. It suits party posters, classroom displays, planning a print before paying for it, and anything temporary.
- A print shop prints one seamless sheet on photo paper with calibrated colour. It costs more, but for something framed and kept, it is worth it. Send them the single large file at 150–200 DPI; shops print posters at those resolutions, and a 300 DPI file of an A1 poster is a very large upload for no visible gain.
Does AI upscaling really help?
Partly, and only for small photos. An AI upscaler predicts the detail that would sit between the pixels it has: edges become crisp instead of blurry, and textures such as hair and fabric look plausible. Our Image Upscaler takes photos up to 2 MP and enlarges them 2× or 4×, up to 16 MP. A 1,000 × 750 photo upscaled 4× becomes 4,000 × 3,000, enough for a decent A2.
What it cannot do is recover detail that was never captured. Small faces, distant text and fine patterns can come back smoothed or subtly invented, so check the result at 100% zoom before printing. And if your photo is already 12 MP, the upscaler has nothing to add: choose a smaller poster instead. The Photo to Poster Maker only offers upscaling when the print would be below 200 DPI, and tells you when it would not help.
Before you print
- Use the original photo, not a messaging-app copy or a screenshot.
- Aim for 150 DPI or more; check the meter after choosing the size.
- Print one test page at Actual size and measure the 10 cm line.
- For a print shop, ask which resolution they want; if they ask for “300 DPI” on a file you already sized, the Change Image DPI tool sets the number without touching the pixels.
