Convert an image to 300 DPI by adding real pixels

DPI stands for dots per inch. In print shop instructions it almost always means pixels per inch (PPI): how many pixels of your image land on each inch of paper. 300 is the standard for photos, cards and books held at reading distance, because at that density single pixels are too small to see.

An image file has no fixed physical size. A 2400 x 3000 pixel photo is 8 x 10 inches at 300 DPI, 16 x 20 inches at 150 DPI, or about 33 x 42 inches at 72 DPI. The pixels are the same in all three cases. The DPI number in the file only says how large to print it.

Most editors let you change the DPI value without changing the pixels. In Photoshop this is Image Size with Resample turned off, and many free online converters do the same. The file then says 300 DPI, but either the print size shrinks to match, or the printer stretches the same pixels over the same paper. Either way the print gains no detail.

Some print services only read the DPI field, so changing it may get a file past an upload form. It will not make the print sharper. If a shop warns that your image is low resolution, the warning is about the pixel count.

Multiply each side of the print in inches by 300. An 8 x 10 needs 2400 x 3000 pixels. For metric paper, divide millimetres by 25.4 first: A4 is 210 x 297 mm, which is 8.27 x 11.69 inches, or 2480 x 3508 pixels at 300 DPI.

If your image already has that many pixels or more, set the DPI field to 300 and you are done. If it has fewer, you need more pixels, and that is where upscaling comes in. The print size chart lists the targets at 240 and 150 PPI as well.

Divide the target by your image size to find the factor you need. If it is four or less, one run of Upscale 4× is enough; it accepts images up to 5 MP. For example, a 700 x 875 photo for an 8 x 10 needs a factor of about 3.4. Upscale it 4× to 2800 x 3500, then print it at about 350 DPI or reduce it to exactly 2400 x 3000.

If the factor is between four and eight, use Upscale 8×. It accepts images up to 1.25 MP and uses 2 credits per photo. Both models give results up to 80 MP, which covers a 24 x 36 inch print at 300 DPI.

Clean the image first if it is grainy or has compression blocks, because upscaling enlarges them. Enhance removes noise and compression damage at the same size. After upscaling, check that the pixel size reaches the target, and set the DPI field to 300 if the shop's form asks for it. That last step only changes the label, but now the label is true.

The upscalers rebuild sharp edges and add natural fine texture so the enlarged photo does not look smeared. That makes the print look clean at 300 DPI. It does not turn a small photo into one taken with a better camera. Faces that are tiny in the original stay soft, and small text stays as soft as it was, because the models do not guess letters.

Large prints are seen from farther away, so lower densities look the same to the eye. For posters and canvases, 150 DPI is usually fine and 200 DPI gives a margin. Our poster size guide has those numbers.

If the image is very small, such as a 300-pixel thumbnail, no method produces a 300 DPI letter-size print that looks like a real photo. Choose a smaller print size instead.