Your phone photo is big enough. Here is the arithmetic
A 12 megapixel phone photo, printed on A4 as an 88-piece puzzle, lands at 263 dots per inch. That is print quality. The same file on A3 lands at 179, and on A1 at 85. Nothing about the photo changed — only how far it was stretched.
Dots per inch is a division: pixels across, divided by inches across. A 3000-pixel-wide file printed 10 inches wide is 300 dpi. Printed 20 inches wide it is 150 dpi. The file has not degraded; it has been asked for twice as much.
What 300 dpi means in pixels
300 dpi is the convention for a photograph you look at from about 25 cm, which is why magazines and photo labs use it. A jigsaw is not looked at from 25 cm — it is handled at arm’s length, and it is cut into 20 mm squares. That is why 200 dpi is a defensible floor here, and why a sheet at 260 dpi from a phone is not a compromise at all.
The two columns below are the same picture block, measured in millimetres by the generator, converted at both resolutions. Multiply millimetres by dpi and divide by 25.4 and you get the pixel count a file needs to print without upscaling.
| Sheet and grid | Picture block | At 300 dpi | At 200 dpi | Megapixels at 300 |
|---|---|---|---|---|
| A4 · 6 × 8 | 190 × 253 mm | 2244 × 2992 | 1496 × 1995 | 6.7 MP |
| A4 · 8 × 11 | 188 × 259 mm | 2225 × 3059 | 1483 × 2039 | 6.8 MP |
| A4 · 10 × 14 | 185 × 259 mm | 2185 × 3059 | 1457 × 2039 | 6.7 MP |
| A3 · 10 × 14 | 273 × 382 mm | 3223 × 4512 | 2148 × 3008 | 14.5 MP |
| A2 · 16 × 23 | 387 × 556 mm | 4568 × 6567 | 3046 × 4378 | 30.0 MP |
| A1 · 24 × 34 | 567 × 803 mm | 6695 × 9484 | 4463 × 6323 | 63.5 MP |
The block, not the paper, is what your photo has to fill. On A4 the block is 190 × 253 mm inside a 210 × 297 mm sheet — the 10 mm margin and the 18 mm footer take the rest, and they cost you pixels you were counting on.
What a phone actually gives you
A 12 megapixel sensor produces 4032 × 3024 pixels. That is 12.2 million pixels arranged 4:3. Change the camera app to 3:2 and you get 4032 × 2688, which is still called 12 megapixel and is 10.8 million real ones.
Against the 6.8 MP that A4 wants, either is comfortably enough. This is the least surprising result on the page, and it is worth stating plainly because most people arrive worried about it: any phone from the last decade is sufficient for A4.
The crop nobody counts
Here is where the arithmetic gets less generous. The picture block is portrait — 188 × 259 mm is an aspect of 0.73. A photo shot in landscape has to lose its sides to fill that, and the loss is real pixels, not empty margin.
| Source file | A4 · 8 × 11 | A3 · 10 × 14 | A2 · 16 × 23 |
|---|---|---|---|
| 12 MP, 4:3 (4032 × 3024) | 297 dpi | 201 dpi | 138 dpi |
| 12 MP, 3:2 (4032 × 2688) | 263 dpi | 179 dpi | 123 dpi |
| 48 MP, 4:3 (8000 × 6000) | 588 dpi | 399 dpi | 274 dpi |
Same sensor size, 4:3 against 3:2, is a 13% difference in effective resolution on a portrait sheet — because the taller frame keeps more of the pixels that survive the crop. If you are choosing a camera setting for a puzzle, choose 4:3.
That 13% is why two people with “the same 12 megapixel phone” get different results, and why the honest answer to “is my photo big enough” is a number rather than a yes.
When it stops being enough
At 200 dpi the print is sharp at arm’s length. At 150 it starts to look soft if you know what to look for, and at 100 the print has visible stair-stepping on high-contrast edges — a window frame, a shirt collar, the edge of a face against a bright sky.
A jigsaw hides softness better than a poster does, for two reasons: the cut lines run across the image every 20 mm, and nobody holds a piece at reading distance for long. So a 12 MP phone photo on A3 at 179 dpi is a good print. The same file on A1 at 85 dpi is not — the stretch is close to four times linear, and no amount of sharpening invents detail that the sensor did not record. Upscaling makes the file bigger and the print softer.
Check your own file in ten seconds
Open the photo’s properties and read the pixel dimensions. Then multiply the picture block width from the table above by your target dpi and divide by 25.4. If your file is wider than the result, you are printing at full resolution or better.
Or skip the arithmetic: the generator shows the pixel count it needs for the sheet you have chosen, and warns when the file is short. It does not upscale silently and call it fine.
The short version, for the sheet most people print: A4 is safe from any phone, A3 is safe from a 14 MP file and usually fine from 12, A2 wants a modern high-resolution phone or a camera, and A1 wants a print shop and a proper file.
A4 is the safe answer, and the cheap one
One sheet, 48 pieces, 31.7 mm each, printed from a phone photo without any upscaling.