Resolution, DPI, PPI — these terms get thrown around interchangeably, but they describe different things. Mixing them up leads to images that look blurry when printed or unnecessarily large on the web. Here is what each term means and when it matters.
Pixels are the foundation
A digital image is a grid of pixels. A 1920×1080 image is 1,920 pixels wide and 1,080 pixels tall — that is roughly 2 million individual color dots. The pixel dimensions are the only truly fixed property of a digital image. Everything else (print size, resolution, DPI) is derived from them.
Resolution vs DPI vs PPI
Resolution refers to the total pixel dimensions of an image — its width and height in pixels. A 4000×3000 image has higher resolution than a 1200×900 image because it contains more pixel data.
PPI (Pixels Per Inch) describes how those pixels map to physical space. A 300 PPI setting means 300 pixels fit into one inch of print. The same 600-pixel-wide image printed at 300 PPI produces a 2-inch-wide print. Printed at 72 PPI, that same image produces an 8.3-inch print. The pixels did not change — only the physical interpretation changed.
DPI (Dots Per Inch) is a printer term. It describes how many ink dots a printer places per inch. Higher DPI generally means finer detail in printed output. For screen work, DPI is mostly irrelevant because screens display at their native pixel density regardless of what the image metadata says.
When resolution matters
For the web: Pixel dimensions are what count. A 1200×800 image displays as 1200×800 pixels in the browser regardless of its DPI metadata. Setting an image to 300 DPI does not make it look sharper on screen. What matters is matching the image dimensions to the display space — serving a 4000-pixel image in a 600-pixel container wastes bandwidth without improving visual quality.
For print: DPI and pixel dimensions both matter. A 300 DPI setting is the standard for quality print output. To determine if your image is print-ready, divide the pixel dimension by the desired DPI: a 3000-pixel-wide image prints at 10 inches at 300 DPI, or 41 inches at 72 DPI.
For screenshots: Screenshots capture at your screen's native resolution. A 2x Retina screenshot of a 1440-pixel browser window produces a 2880-pixel image. If you resize that down to 1440 for documentation, you are effectively reducing the resolution.
Practical takeaway
For screen use, resize images to the exact pixel dimensions you need. For print, ensure the pixel count supports your target DPI at the desired physical size. Do not change DPI metadata expecting it to magically improve on-screen appearance — it does not work that way.