PPI Calculator
Pixel density of a screen from its resolution and diagonal, with its width, height, dot pitch and aspect ratio.
Your screen
Filled in with example values. Replace them with your own.
Results update as you type.
Result
1920×1080 at 24 in: 91.79 PPI (36.14 pixels per cm), dot pitch 0.277 mm
Pixel density
91.79PPI
- Pixels per centimetre
- 36.14
- Dot pitchDistance between pixel centres
- 0.277 mm
- Screen width
- 20.92 in · 53.13 cm
- Screen height
- 11.77 in · 29.89 cm
- Aspect ratio
- 16:9 (1.78:1)
- Total pixels
- 2,073,600 (2.07 MP)
How it’s calculated
Diagonal in pixels
√(1920² + 1080²) = 2,202.9 px
PPI
2,202.9 ÷ 24 = 91.79
Dot pitch
25.4 mm ÷ 91.79 = 0.277 mm
How the PPI calculator works
Enter the screen resolution in pixels and the diagonal size. The calculator finds the diagonal in pixels with Pythagoras’ theorem and divides it by the diagonal in inches. It also works out the physical width and height of the screen, the dot pitch and the aspect ratio.
The formula
Diagonal in pixels = √(Width² + Height²)
PPI = Diagonal in pixels ÷ Diagonal in inches
Dot pitch = 25.4 mm ÷ PPI
1 inch = 2.54 cm exactly.
Worked examples
- A 24-inch screen at 1920 × 1080: √(1920² + 1080²) = 2,202.91 pixels ÷ 24 = 91.79 PPI, a dot pitch of 0.2767 mm. The screen is about 20.92 × 11.77 inches.
- A 27-inch screen at 3840 × 2160: 4,405.81 ÷ 27 = 163.18 PPI.
Assumptions
- Pixels are square, as on almost all modern screens.
- The diagonal is the visible screen area. If the size you enter is rounded, the PPI changes slightly.
Frequently asked questions
What is PPI?
Pixels per inch: how many pixels fit along one inch of the screen. The higher it is, the smaller each pixel and the sharper text and images look at the same viewing distance.
Is a higher PPI always better?
Up to a point. How sharp a screen looks also depends on how far away you sit: a TV seen from across a room can have a much lower PPI than a phone held close and still look sharp.
What is dot pitch?
The distance between the centres of two neighbouring pixels, usually in millimetres. It is simply 25.4 mm divided by the PPI.
Why is 3440 × 1440 shown as 43:18 and not 21:9?
The calculator shows the exact ratio of the pixel counts. 3440 ÷ 1440 = 2.39, which is close to but not exactly 21 ÷ 9 = 2.33; “21:9” is a marketing name for screens of roughly this shape.