PPI Calculator
- 108.79
- Pixels per inch
- 0.2335
- Dot pitch (mm)
- 597.7
- Screen width (mm)
- 336.2
- Screen height (mm)
Standard density
Typical for a desktop monitor viewed at arm’s length, where about 90 to 110 PPI has been the norm for two decades.
The PPI calculator works out pixel density from a screen’s resolution and diagonal size, along with dot pitch and the physical width and height. Screens are sold by diagonal inches, which tells you nothing about sharpness on its own, a 27-inch 1080p display and a 27-inch 4K display are the same size and look completely different.
How it works
PPI = sqrt(width^2 + height^2) / diagonal
- sqrt(w² + h²)
- the diagonal measured in pixels, by Pythagoras
- diagonal
- the advertised screen size in inches
- Dot pitch is the distance between pixel centres, 25.4 / PPI in millimetres.
- Physical width and height come from scaling the pixel dimensions by the same factor that maps the pixel diagonal to the inch diagonal.
- Roughly 90 to 110 PPI has been the desktop monitor norm for two decades; phones exceed 400.
PPI and DPI are used interchangeably in casual speech but mean different things: PPI describes a display, DPI describes a printer’s ink dots. A 300 DPI print and a 300 PPI screen are not comparable measures of detail.
Examples
A 27-inch 1440p monitor
Resolution
2560 × 1440
Diagonal
27 inches
Result
PPI 108.79 · Dot pitch 0.2335 mm · 596.7 × 335.7 mm
Just under 109 PPI, which is the sweet spot most desktop monitors have targeted for years.
The same size at 4K
Resolution
3840 × 2160
Diagonal
27 inches
Result
PPI 163.18
The physical dimensions are identical to the example above. Only the pixel density changes. This is why diagonal size alone says nothing about sharpness.
Frequently asked questions
What PPI is high enough?
It depends entirely on viewing distance. A phone held 30 cm away needs 300 PPI or more before pixels stop being resolvable; a monitor at arm’s length is comfortable around 110; a billboard viewed from across a road can be under 10. Density and distance trade off directly.
Is PPI the same as DPI?
No, though the terms are used interchangeably. PPI is pixels per inch on a display; DPI is dots of ink per inch on a printer, and printers use multiple dots to render one pixel’s colour. A 300 DPI print is not equivalent to a 300 PPI screen.
Why is my screen’s calculated size slightly different from the advertised one?
Because manufacturers round the diagonal. A "27-inch" monitor is usually 27.0 or 26.9 inches of visible area, and some quote the panel size including a bezel-covered edge. The calculated width and height will be within a millimetre or two.
What is dot pitch used for?
It is the older way of expressing the same information, the physical distance between pixel centres. Monitor specifications quoted it before PPI became standard, and CRT-era displays around 0.28 mm are roughly equivalent to 91 PPI.