About the PPI Calculator
This PPI calculator works out the pixel density of any display — monitor, laptop, phone, tablet or TV — from its resolution in pixels and its diagonal size. Along with pixels per inch it gives the dot pitch (the distance between pixel centres), the physical width and height of the panel, the aspect ratio, the total megapixels and the distance at which individual pixels become invisible to normal eyesight.
It is useful when comparing monitors with different sizes and resolutions, choosing a scaling factor for a desktop, checking whether a phone screen will look sharp, or preparing artwork and UI assets for a specific device. The comparison table shows how the same resolution would look on other common screen sizes.
The calculation assumes square pixels and that the advertised diagonal is the visible image area, which is true for almost all modern screens. Manufacturers often round the diagonal (a "27-inch" panel may measure 27.0 or 26.9 inches), so results can differ slightly from spec sheets.
With the default inputs, the pixel density is 108.79 PPI. Change any value above to recalculate instantly.
How to use the ppi calculator
- 1Enter the horizontal and vertical resolution in pixels (for example 2560 × 1440).
- 2Enter the diagonal screen size and choose inches or centimetres.
- 3Read the pixel density (PPI) and dot pitch.
- 4Check the physical width, height and aspect ratio of the panel.
- 5Use the table to compare the same resolution on other screen sizes.
Formula and method
Pixel density is the number of pixels along the diagonal divided by the diagonal length in inches. The diagonal pixel count comes from Pythagoras: √(W² + H²). Because pixels are square, the same density applies horizontally and vertically, so the physical width is W ÷ PPI and the height is H ÷ PPI.
Dot pitch converts the density to millimetres per pixel (25.4 mm per inch ÷ PPI). The "retina" distance is where one pixel subtends one arcminute — the resolving limit of 20/20 vision — found as 1 ÷ (PPI × tan(1/60°)), roughly 3438 ÷ PPI inches. A diagonal entered in centimetres is divided by 2.54 first.
- W
- Horizontal resolution in pixels
- H
- Vertical resolution in pixels
- D
- Diagonal screen size in inches
- 1′
- One arcminute (1/60 of a degree)
Worked examples
27-inch 1440p monitor
The diagonal is √(2560² + 1440²) = 2,937.2 pixels. Dividing by 27 inches gives 108.8 PPI, a dot pitch of 0.2335 mm and a visible area about 23.5 × 13.2 inches. Pixels blend together beyond roughly 31.6 inches.
32-inch 4K monitor
A 4K panel has 4,405.8 diagonal pixels; over 32 inches that is 137.7 PPI. The screen is about 70.8 × 39.8 cm, holds 8.29 megapixels and looks pixel-free from about 25 inches away.
6.1-inch phone (2556 × 1179)
A 2556 × 1179 phone screen has 2,814.8 diagonal pixels packed into 6.1 inches — about 461 PPI with pixels just 0.055 mm apart. At normal phone viewing distances (10–12 in) the pixels are far beyond what the eye can resolve.
Laptop measured in centimetres
A 39.624 cm diagonal is 15.6 inches. A Full HD panel of that size has 2,202.9 diagonal pixels, so the density is about 141.2 PPI.
Frequently asked questions
What is a good PPI for a monitor?+
For desktop monitors viewed at 50–70 cm, about 90–110 PPI looks fine at 100% scaling, and 140–220 PPI looks noticeably sharper with 150%–200% scaling. Laptops usually run 130–230 PPI and phones 300–500 PPI because they are held closer.
Is PPI the same as DPI?+
Not strictly. PPI (pixels per inch) describes a screen or digital image, while DPI (dots per inch) describes how many ink dots a printer lays down. People often use DPI loosely for screens, and for displays the two numbers are treated as the same thing.
What is dot pitch?+
Dot pitch is the distance between the centres of two adjacent pixels, usually given in millimetres. It is simply 25.4 ÷ PPI, so a 109 PPI monitor has a dot pitch of about 0.233 mm; smaller numbers mean a sharper screen.
What does "retina" distance mean?+
It is the viewing distance at which one pixel covers one arcminute of your field of view — roughly the finest detail 20/20 vision can separate. Beyond that distance the screen looks continuous; closer in, sharp-eyed viewers may see pixels or jagged edges.
Why does my result differ slightly from the manufacturer’s spec?+
Advertised diagonals are often rounded (a 23.8-inch panel may be sold as 24-inch) and some specs quote the nominal rather than viewable size. Use the exact viewable diagonal from the data sheet for the most accurate PPI.