People often say "high resolution" without saying what they mean. For screens, resolution is the number of pixels. DPI only matters when you print.
Pixels are what screens care about
A website, app or social network looks at the width and height in pixels. A 1920 × 1080 image is 1920 pixels wide and 1080 tall, whatever its DPI number says.
DPI only matters for print
DPI means dots per inch. It links pixels to a physical size on paper: pixels = inches × DPI. A 4 × 6 inch photo printed at 300 DPI needs 1200 × 1800 pixels.
How many pixels do I need?
- Web page or social post: match the size shown, often 1080 to 2000 pixels wide.
- Full HD screen: 1920 × 1080. 4K: 3840 × 2160. 8K: 7680 × 4320.
- Photo print at 300 DPI: inches × 300 on each side.
- Large poster viewed from far away: 100 to 150 DPI is often enough.
Changing DPI does not change quality
Changing the DPI number in a file does not add detail. Only the pixel width and height decide how sharp a picture can be. If you need a bigger print, you need more pixels, and a small photo cannot be made sharper by enlarging it.
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