What is my screen’s PPI?
Type the screen resolution in pixels and its diagonal size. The PPI calculator gives the pixel density in pixels per inch, the dot pitch and the size of the screen.
- Pixel density
- 91.79
A 24 in screen at 1,920 × 1,080 pixels has 91.79 pixels per inch.
- Dot pitchmm
- 0.2767
- Diagonal in pixels
- 2,202.91
- Screen width
- 20.92 in
- Screen height
- 11.77 in
- Aspect ratio
- 16:9
- Total pixelsMP
- 2.07
Pixel density: 91.79. A 24 in screen at 1,920 × 1,080 pixels has 91.79 pixels per inch.
How to calculate
Computes a screen’s pixel density in pixels per inch (PPI) from its resolution and diagonal size, with the dot pitch, the screen’s width and height, and its aspect ratio.
Example with the default inputs (Horizontal pixels 1,920, Vertical pixels 1,080, Diagonal size 24 in): A 24 in screen at 1,920 × 1,080 pixels has 91.79 pixels per inch.
Method: PPI = √(width² + height²) ÷ diagonal (inches); dot pitch = 25.4 ÷ PPI mm; screen width = diagonal × width ÷ √(width² + height²).
- Pixels are square, so the same density holds across and down the screen.
- The diagonal is the visible area, corner to corner; screens with rounded corners are measured as the full rectangle.
Worked examples
Each example is checked against the calculator on every build.
- Horizontal pixels 1,920, Vertical pixels 1,080, Diagonal size 24 in gives Pixel density 91.787799, Dot pitch 0.276725, Diagonal in pixels 2,202.90717, Aspect ratio 16:9, Total pixels 2.0736.Source: NIST SP 811, Appendix B (1 in = 25.4 mm exactly), https://www.nist.gov/pml/special-publication-811
- Horizontal pixels 2,556, Vertical pixels 1,179, Diagonal size 6.12 in gives Pixel density 460.Source: Apple, iPhone 15 Technical Specifications (6.1-inch display, 6.12 in as a rectangle; 2556 × 1179 pixels at 460 ppi), https://support.apple.com/en-us/111831 (460 ppi, rounded to a whole ppi, so within 0.5 ÷ 460)
- Horizontal pixels 3,840, Vertical pixels 2,160, Diagonal size 27 in gives Pixel density 163.178309, Screen width 23.53 in.Source: NIST SP 811, https://www.nist.gov/pml/special-publication-811
How it works
Let w and h be the horizontal and vertical pixel counts and D the diagonal in inches.
- Diagonal in pixels = √(w² + h²).
- Pixel density PPI = √(w² + h²) ÷ D.
- Dot pitch = 25.4 ÷ PPI, in millimetres.
- Screen width = D × w ÷ √(w² + h²); screen height = D × h ÷ √(w² + h²).
- Aspect ratio = w : h divided by their greatest common divisor (1920 : 1080 is 16:9).
- Total pixels = w × h ÷ 1,000,000, in megapixels.
A diagonal typed in centimetres is converted with 1 in = 2.54 cm exactly.
Rules. Pixel counts are whole numbers from 1 to 100,000. The diagonal is from 0.1 in to 1,000 in (0.254 cm to 2,540 cm). Every pair of values in range has an answer.
Output format. Decimals and significant figures below are the most shown; trailing zeros are dropped (23.0 shows as 23, money keeps its cents). PPI, the pixel diagonal and megapixels show 2 decimals; dot pitch 4 decimals in mm; screen width and height 2 decimals in inches (centimetres in Metric). Each is rounded half up from its decimal value; values are computed in double precision.
Assumptions
- Pixels are square, which is true of almost every modern screen.
- The diagonal is the visible area, corner to corner.
Worked examples by hand
A 24 in full-HD monitor. √(1920² + 1080²) = √4,852,800 = 2,202.91. PPI = 2,202.91 ÷ 24 = 91.79. Dot pitch 25.4 ÷ 91.79 = 0.2767 mm. Aspect ratio 16:9; 2.07 MP.
iPhone 15. √(2556² + 1179²) = 2,814.81; ÷ 6.12 in = 459.94, which Apple quotes as 460 ppi.
A 27 in 4K monitor. √(3840² + 2160²) = 4,405.81. PPI = 163.18. Width = 27 × 3,840 ÷ 4,405.81 = 23.53 in; height = 27 × 2,160 ÷ 4,405.81 = 13.24 in.
Other questions people ask
How do I calculate PPI?
Find the diagonal in pixels with Pythagoras, √(width² + height²), and divide by the diagonal in inches. A 24 in 1920 × 1080 monitor has √(1920² + 1080²) = 2,202.9 pixels across its diagonal, so 2,202.9 ÷ 24 = 91.79 PPI.
What is a good PPI?
It depends on how far away you sit. Desktop monitors at arm’s length are often 90 to 165 PPI (24 in full HD is 92, 27 in 4K is 163); phones held closer are often 400 to 500 PPI. Higher PPI makes text look sharper at the same distance.
Is PPI the same as DPI?
Not quite. PPI counts the pixels a screen shows per inch; DPI counts the ink dots a printer lays down per inch. People often say DPI for both. To size an image for print, use the DPI calculator.
Why does my phone say 460 ppi when I get 459.9?
Makers round the density and quote a rounded diagonal. Apple quotes the iPhone 15 as a 6.1 in screen, but 6.12 in when measured as a full rectangle; 2556 × 1179 pixels over 6.12 in gives 459.9, which Apple rounds to 460 ppi.
What is dot pitch?
The distance between the centres of two neighbouring pixels: 25.4 mm ÷ PPI. A 91.79 PPI monitor has a dot pitch of 0.2767 mm. A smaller pitch means a finer screen.
How do I find a screen’s width and height in inches?
Scale the diagonal by each side’s share of the pixel diagonal: width = diagonal × horizontal pixels ÷ diagonal pixels. A 27 in 3840 × 2160 screen is 27 × 3,840 ÷ 4,405.8 = 23.53 in wide.