DPI for printing: how many pixels does your photo need

The sum that settles it

Pixels needed = size in inches × dpi. An inch is 25.4 mm. If you want to print at 300 dpi (the figure most photo labs ask for high-quality prints viewed at reading distance), each inch of paper needs 300 pixels of image.

An A4 sheet measures 210 × 297 mm, which is 8.27 × 11.69 inches. At 300 dpi that is 8.27 × 300 = 2,480 pixels wide and 11.69 × 300 = 3,508 high: an image of about 8.7 megapixels. At 150 dpi, 1,240 × 1,754 is enough. And the other way round: a 4,000 × 3,000 pixel photo (12 megapixels, typical of a phone) gives, at 300 dpi, a print of 33.9 × 25.4 cm, slightly bigger than a landscape A4.

Pixels by print size

Notice that 150 dpi on an A2 needs the same pixels as 300 dpi on an A4. That is why a large poster can be printed at fewer dpi than a hand-held photograph: it is viewed from farther away, and individual dots are harder to see.

What dpi is "enough"

There is no single official threshold, but there are rules of thumb nearly everyone uses:

• 300 dpi: quality printing that will be looked at closely (photos, magazines, leaflets, cards).
• 150 dpi: acceptable for posters or banners viewed from farther away, and sometimes enough for a home print.
• 72 or 96 dpi: screen values, not print values. At those, fine text and edges look stepped.

The farther away a print is viewed, the less resolution it needs. A billboard can have very few dpi and still look fine from the road.

Why changing an image's dpi does not improve it

An image file can carry a "dpi" tag among its metadata. That tag is only a suggested print size; it does not change the pixels. An 800 × 600 pixel image tagged as 300 dpi prints at 6.8 × 5.1 cm; tagged as 72 dpi, at 28.2 × 21.2 cm. In both cases it has the same 800 × 600 pixels, and enlarged it will look equally blurry. What matters is the number of pixels. If an image is small, setting it to "300 dpi" in a program only reinterprets the tag, or invents pixels by interpolation (which smooths but does not add detail).

And on screen

On screen dpi does not apply in the same way. A CSS pixel is defined as 1/96 of an inch, but on modern high-density screens one CSS pixel covers several physical dots. For a web image what counts is the dimensions in pixels (say, 1,200 px wide) and the file size, not the dpi in the metadata.

"dpi" and "ppi": a naming muddle

Strictly, ppi (pixels per inch) is the pixel density of an image or a screen, and dpi (dots per inch) is that of a printer, which uses several ink dots to form a pixel. In practice almost everyone, labs and programs included, says "dpi" for both. What matters is the sum above.

How to check whether your image holds up

1. Look at the image's dimensions in pixels (in the file properties).
2. Divide them by 300 (or 150 for a poster) to get the maximum size in inches, and by 118.1 (pixels per centimetre at 300 dpi) for centimetres.
3. The DPI and print size calculator does that sum, and the print size preview shows how it would look at real size.
4. If the image falls short, the image quality checker tells you whether it suits the use you have in mind, and if you need to reduce the print size, the image resizer sets exact dimensions.

One last caution: screens and printers do not show colours the same way (print uses CMYK and screens use RGB), so the printed result may look a little less vivid than on the monitor. Print a small test before ordering many copies.

Before printing, it helps to know which format to use: JPG, PNG, WebP or AVIF. And if the photo is for an official document, see passport photo size requirements for the exact dimensions.

Sources and further reading

• MDN Web Docs: CSS data type (1px = 1/96 of an inch)

Figures checked on 3 October 2026.