PPI Calculator: Pixels Per Inch, Dot Pitch & Screen Size

How to use the PPI calculator

Pick a screen from Common screens, or type the horizontal and vertical resolution in pixels.
Enter the diagonal size from the spec sheet, in inches or centimetres.
Press Use my screen to fill in this device's resolution; add its diagonal (the screen size page can measure it).
Read the PPI and the other values; they update as you type.

What the results mean

PPI (pixels per inch) is the diagonal in pixels divided by the diagonal in inches: PPI = √(width² + height²) / diagonal. A 27 inch 2560 x 1440 monitor has √(2560² + 1440²) = 2937 pixels across its diagonal, so 2937 / 27 = 108.8 PPI.

Dot pitch is the distance between the centres of two pixels, 25.4 / PPI in millimetres. Smaller is sharper.
Pixels vanish beyond is the distance at which one pixel covers one arcminute, the detail limit of 20/20 vision. Further away than this, a person with normal sight cannot see single pixels. Apple's "Retina" idea is based on the same calculation.
Screen size is the width and height of the picture, worked out from the diagonal and the pixel ratio.

Screen	Typical PPI
55-65 inch 4K TV	68-80
24 inch 1080p monitor	92
27 inch 1440p monitor	109
27 inch 4K monitor	163
Laptops (Full HD to Retina)	140-260
Phones	400-500

How much PPI do you need?

It depends on how far away you sit. A desktop monitor at 60-70 cm looks sharp from about 110 PPI and very sharp from 160 PPI; that is why a 27 inch 1440p monitor is popular and 4K is the step up. Laptops sit closer, so 200 PPI and above looks clean. Phones are held at 25-30 cm and need 400 PPI or more for pixels to disappear. TVs are watched from 2-3 metres, where 70-80 PPI on a 4K set is already beyond what the eye can resolve; 8K adds little at normal distances.

High PPI is not free: it needs display scaling (often 150-200%) to keep text readable, and in games it needs a stronger graphics card. See your current scaling on the screen resolution page.

PPI and DPI

PPI describes screens: how many pixels sit in an inch of the panel. DPI (dots per inch) describes printers, which build each pixel from many tiny ink dots, and it is also used loosely for mouse sensitivity, which is a different thing again (counts per inch of movement; see the DPI analyzer). For printing, 300 pixels per inch of the printed size is the usual target for photos.

Common problems and fixes

The PPI does not match the spec sheet

Spec sheets round the diagonal (a "27 inch" monitor is often 27.0 to 27.2 inches) and some round the PPI. A difference of 1-2% is normal.

Use my screen gives the wrong resolution

The browser reports the screen this window is on, multiplied by the pixel ratio. Reset browser zoom to 100% (Ctrl+0) and make sure the window is on the right monitor.

I only know the size in centimetres

Choose cm as the unit. The calculator converts it to inches for you.

Frequently asked questions

How do I calculate PPI?

Square the width and height in pixels, add them, take the square root, and divide by the diagonal in inches. The calculator does it for you.

What is a good PPI for a monitor?

About 110 PPI is sharp at normal desk distance, and 140-165 PPI is very sharp. Less than 90 PPI shows visible pixels up close.

What is the PPI of a 27 inch 4K monitor?

About 163 PPI. A 27 inch 1440p monitor is about 109 PPI and a 27 inch 1080p one about 82 PPI.

What is Retina display PPI?

Apple calls a screen Retina when single pixels cannot be seen at the normal viewing distance. That is around 220 PPI for laptops and 300-460 PPI for phones.

Is higher PPI always better?

Higher PPI gives sharper text and images but needs display scaling and more graphics power. Beyond the distance where pixels vanish, extra PPI makes little visible difference.

What is dot pitch?

The distance between two pixel centres, in millimetres. A 24 inch 1080p monitor has a dot pitch of about 0.277 mm.