Formula
PPI = √(width² + height²) ÷ diagonal. The width and height of the screen come from the same triangle: width = diagonal × pixel width ÷ diagonal in pixels.
Examples
A 24-inch Full HD monitor (1920 × 1080) has 91.79 PPI and measures 20.92 × 11.77 in. A 27-inch QHD monitor (2560 × 1440) has 108.79 PPI, which is why text looks sharper on it.
How much PPI do I need?
- Desktop monitors at arm’s length: about 90 to 110 PPI is comfortable; 140 or more looks very sharp.
- Phones are held closer, so they use 400 PPI or more.
- TVs are watched from far away, so a 4K TV of 65 inches has only about 68 PPI.
The last line of the result shows from what distance your eyes can no longer see single pixels.
Frequently asked questions
Is PPI the same as DPI?
PPI is pixels on a screen; DPI is ink dots on paper. People often mix them up, but for screens PPI is the right term.
Why is 2560 × 1080 called 21:9?
The exact ratio is 64:27 (2.37:1). Ultrawide monitors are sold as 21:9 because it is close and easy to remember.
See also
Results are estimates for information only and are not financial, legal or medical advice. Rates, taxes and fees vary — confirm with a professional or your lender.