PPI Calculator
Work out pixels per inch, dot pitch and physical size for any screen. Compare up to three screens side by side, or find the size you need for a target pixel density.
Pixel density calculator
109 PPI: Standard desktop density. Text is usually readable at 100% scaling from about 60 to 80 cm.
Compare screens (3 of 3)
| Screen | PPI | Dot pitch | Size (in) | Area | MP |
|---|---|---|---|---|---|
| A: 27" 1440p QHD | 108.8 | 0.233 mm | 23.5 × 13.2 | 312 in² | 3.69 |
| B: 27" 4K UHDSharpest | 163.2 | 0.156 mm | 23.5 × 13.2 | 312 in² | 8.29 |
| C: 32" 4K UHD | 137.7 | 0.184 mm | 27.9 × 15.7 | 438 in² | 8.29 |
Reverse: size for a target PPI
Uses the resolution of Screen A (2560 × 1440).
Formulas: PPI = √(w² + h²) ÷ diagonal in inches. PPCM = PPI ÷ 2.54. Dot pitch = 25.4 ÷ PPI mm. Width and height follow from the aspect ratio and that diagonal. These use the resolution and size you typed. This is not the operating system's DPI setting and not Windows scaling. Results assume square pixels and the advertised diagonal, which is often rounded (a "27 inch" panel may measure 26.9).
Pixel density explained
What PPI means and what counts as good
Pixels per inch is how many pixels sit along one inch of the panel when the pixels are square. It is the diagonal pixel count divided by the diagonal in inches. Higher PPI means smaller pixels, and whether you can see them depends on distance. Phones are held close, and many are around 300 to 500 PPI. Laptops at arm's length often fall between about 150 and 220 PPI. Desktops viewed from 60 to 80 cm are often about 90 to 160 PPI. A 65 inch 4K TV is about 68 PPI. One pixel on that panel spans 1 arcminute at about 1.3 metres, so from 2 metres or further a 20/20 eye should not separate single pixels.
How 27 inch 1440p compares
A 27 inch 2560 × 1440 monitor lands at about 109 PPI. A 24 inch 1080p screen is about 92 PPI, so the 27 inch panel is sharper, not the same density. Both are still readable at 100% scaling. A 27 inch 4K panel is about 163 PPI. It is sharper, and people often turn scaling up to about 150% so text stays a comfortable size, which gives crispness rather than extra workspace. A 32 inch 4K panel is about 138 PPI, between those two. Scaling is an operating-system choice. This calculator does not read it.
PPI and viewing distance
Your eye sees angles, not inches. Double the distance and you need about half the PPI for the same apparent sharpness. A spec sheet that only quotes PPI leaves the distance out. For the distance where one pixel spans 1 arcminute, enter the resolution and size in the Retina display calculator.
Print DPI is not screen PPI
DPI (dots per inch) belongs to printers, which build each colour from many tiny ink dots, so a 1200 DPI printer does not show 1200 image pixels per inch. Screen PPI counts whole pixels. The "72 DPI" or "300 DPI" setting stored in an image file is only a hint for print size and does nothing to how it looks on a monitor. Mouse DPI is a third, unrelated thing.
Related tools
- Retina display calculator: PPI and pixels per degree from a resolution, size and distance you type.
- Aspect ratio calculator: find a ratio, or resize while keeping it.
- What is my screen size: the resolution this browser reports, plus inches after a diagonal or a card match.
- Screen resolution test: CSS pixels and devicePixelRatio, which is not always the panel grid.
Frequently asked questions
How do you calculate PPI?
PPI is the square root of width squared plus height squared, divided by the diagonal in inches. A 2560 × 1440 screen at 27 inches is about 109 PPI. Physical width and height follow from that diagonal and the aspect ratio, assuming square pixels. Every figure uses the resolution and size you typed.
Is this the same as the operating system DPI or Windows scaling?
No. The DPI setting and the scaling percentage change how large text is drawn. This page does not read either one. A 109 PPI monitor can be left at 100% or set to 125% or 150%. The DPI number stored in an image file, and the DPI of a mouse, are separate again.
What is dot pitch?
Dot pitch is the size of one pixel in millimetres: 25.4 divided by the PPI. PPCM is pixels per centimetre, the PPI divided by 2.54. A higher PPI means a smaller dot pitch. Both assume square pixels and the diagonal you entered.
Why do two screens with the same resolution differ?
The same pixel grid on a longer diagonal has a lower PPI. 3840 × 2160 is about 163 PPI at 27 inches and about 138 PPI at 32 inches. The page does not inspect the monitor you are using. Type each resolution and diagonal yourself. An empty comparison row stays as dashes.
What if a field is 0 or blank?
A blank box, zero, a negative number, or any non-numeric value shows a dash. Nothing is divided by zero, and the page does not show Infinity or NaN. A target PPI of 0 does the same in the size solver. A diagonal under 0.5 inches, or a width above 30,000 pixels, also stays as a dash.
How does the target PPI solver work?
It keeps the pixel width and height of the active screen and divides the diagonal pixel count by the target PPI. That gives the diagonal in inches, and the width and height that match it. The target must be from 1 to 3,000. It does not change the screens in the comparison.