DPI and PPI

DPI (dots per inch) and PPI (pixels per inch) both measure resolution: how many dots or pixels are packed into one inch of an image. A higher number means more detail in each inch, so the image looks sharper.

Print and screen

DPI is used for print resolution. It counts the dots of ink a printer places in one inch of paper. PPI is used for screen resolution. It counts the pixels shown in one inch of a display. People sometimes say DPI when they mean PPI on a screen, but the correct term there is PPI.

Quality

A higher resolution gives more detail and higher image quality. At a lower resolution, there are fewer dots or pixels in each inch, so edges and fine detail can look blurred or pixelated. For example, a printed photo at 600 DPI can show the fine fur on a pet, while the same photo at 60 DPI may look soft and blocky.

Resolution and pixel dimensions

Pixel dimensions are the number of pixels across and down an image, such as 2400 wide by 1600 high. Resolution is a separate property: the same 2400 by 1600 image can be set to 250 PPI or 500 PPI. At 250 PPI it is displayed or printed larger, with fewer pixels in each inch; at 500 PPI it is smaller, with more pixels in each inch, so detail looks finer. Changing the PPI setting does not add pixels — it changes how tightly they are packed.