If you’ve ever been told “your image needs to be 300 DPI” and weren’t sure what that meant, you’re in good company. The two terms get used interchangeably online, and that causes real confusion, especially when someone insists a web image must be 72 DPI.
The short version
PPI means pixels per inch. It describes how many pixels of a digital image fit into one inch when it’s displayed or printed at a given size. DPI means dots per inch. It describes how many tiny dots of ink a printer places in one inch. One is about the image, the other is about the printer.
In everyday conversation people say DPI when they mean PPI. That’s fine in casual use, but it’s worth knowing they’re technically different things.
Why a number on its own tells you nothing
Picture a photo that’s 3000 x 2000 pixels. Nothing about that is tied to a physical size yet. Print it at 10 inches wide and you get 300 PPI. Stretch it to 30 inches wide and you get 100 PPI, which will look soft up close. The pixels didn’t change. Only the physical size you spread them across changed.
The formula is simple: pixels divided by inches equals PPI.
Does DPI matter for web images?
Almost never. Screens display images by pixel count. A 1200 x 800 image looks identical whether its metadata says 72 or 300. The “72 DPI for the web” rule is a leftover from early monitors and has no real effect today. What matters on the web is the pixel dimensions and the file size. If you want to understand that side of things, our article on image resolution covers it.
Does DPI matter for print?
Yes, this is where it counts. For prints viewed at arm’s length, about 300 PPI is the common target for sharp results. Large posters and banners that people view from further away can get away with much less, since the eye can’t resolve fine detail at distance. A billboard is often printed at a very low PPI and still looks fine from the road.
Some quick math for common print sizes at 300 PPI:
- 4 x 6 inches needs 1200 x 1800 pixels
- 5 x 7 inches needs 1500 x 2100 pixels
- 8 x 10 inches needs 2400 x 3000 pixels
Changing the DPI number doesn’t change the image
This catches many people out. If you open a 1000 x 1000 pixel image and change its DPI setting from 72 to 300 without resampling, you haven’t added a single pixel. You’ve only changed the label that tells a printer how large to print it, which shrinks the printed size. The image has the same detail it always had. Real extra detail can’t be created this way, which we explain in can you make a low-resolution image higher quality.
What to do in practice
- Making something for a website or social media: ignore DPI, focus on pixel dimensions and file size.
- Making something to print: work out the physical size you want, multiply by 300, and make sure your image has at least that many pixels.
- Not sure? Larger source images are always safer, because you can shrink them but can’t truthfully enlarge them.
Our pixels, inches and centimeters conversion guide has a handy table, and you can resize to exact dimensions with the online image resizer.