PPI Calculator (Pixel Density & DPI)

Calculate a screen’s pixel density (PPI), dot pitch and physical size, plus the print size of an image at any DPI.

How do I calculate the PPI of a screen?

PPI = √(width² + height²) ÷ diagonal in inches. A 27-inch 2560 × 1440 monitor has √(2560² + 1440²) = 2937 pixels on the diagonal, so 2937 ÷ 27 ≈ 108.8 PPI.

Typical pixel densities

Device	PPI
24″ 1080p monitor	≈92
27″ 1440p monitor	≈109
27″ 4K monitor	≈163
Laptop "Retina" displays	≈220–255
Modern phones	≈400–550

The print table shows how large an image of the same pixel size prints: 300 DPI for photo quality, 150 DPI for posters viewed from a distance.

Frequently asked questions

What is the difference between PPI and DPI?

PPI is pixels per inch on a screen or in an image; DPI is ink dots per inch on a printer. They are often used interchangeably for print size.

What is a "retina" distance?

The distance beyond which a person with 20/20 vision can no longer see individual pixels (one pixel per arc-minute).

Can I enter the diagonal in centimetres?

Yes, switch the diagonal unit to centimetres.