DPI and Pixel Dimensions
DPI, dots per inch, sets how many pixels a printed inch contains, and it is the bridge between a paper size in millimetres and an image size in pixels. The same page explains points and picas, the units layout software uses.
At a Glance
| DPI means | Dots (pixels) per printed inch |
|---|---|
| Screen / web | 72 DPI |
| Draft printing | 150 DPI |
| Print quality | 300 DPI |
| Fine-art / photo | 600 DPI |
| Formula | pixels = mm ÷ 25.4 × DPI |
Turning a Size into Pixels
One inch is 25.4 millimetres. To find the pixel dimensions of a paper size, divide each millimetre figure by 25.4 and multiply by the DPI. A4 at 300 DPI: 210 ÷ 25.4 × 300 = 2480 pixels wide, and 297 ÷ 25.4 × 300 = 3508 pixels tall.
Which Resolution Each Job Needs
72 DPI is enough for anything shown only on a screen. 150 DPI is acceptable for a draft print or a document read at arm’s length. 300 DPI is the standard for anything commercially printed and held close, magazines, brochures, photo books. 600 DPI is used for fine-art reproduction and for line art where each edge must stay crisp.
DPI, PPI and the File Itself
A raw image file has a pixel count, not a DPI. DPI only becomes real when you decide how large to print it. The same 2480 × 3508 image is a crisp A4 at 300 DPI or a rough A2 at 150 DPI. Setting a “300 DPI” flag in an editor without changing the pixel count changes nothing about the file.
Upscaling Does Not Add Detail
Enlarging a 1000-pixel image to 3000 pixels gives you a 3000-pixel file, but the extra pixels are interpolated guesses. If a print needs 300 DPI, the source has to carry those pixels from the start, from the camera, the scan or the vector art.
Points and Picas
Layout software measures pages in points and picas rather than millimetres. One point is 1/72 of an inch; one pica is twelve points, or 1/6 of an inch. So an A4 page is 595 by 842 points, and US Letter is 612 by 792. The size pages on this site list the point and pica figure for each format in the dimensions table, next to the millimetre and inch values, so you can paste it straight into a new-document dialog in InDesign, Illustrator or a PDF export preset.
Frequently Asked Questions
How many pixels is A4 at 300 DPI?
2480 × 3508 pixels. At 150 DPI it is 1240 × 1754; at 72 DPI, 595 × 842.
What DPI should I use for printing?
300 DPI for anything printed commercially and held close. 150 DPI is enough for a draft or a large poster viewed from a distance.
Is DPI the same as PPI?
In everyday use, yes. Strictly, PPI is pixels per inch in an image and DPI is ink dots per inch on a press, but most software and most people use them interchangeably.
Does changing DPI change image quality?
Not on its own. DPI is just a print instruction. Quality depends on the pixel count. Raising the DPI number without adding pixels makes the print smaller, not sharper.
✓ Details per the cited standards and the ISO catalogue. Last verified . Editorial Process →