PPI Calculator (Pixels Per Inch)
Enter a screen's resolution and its diagonal size to get its pixel density (PPI), dot pitch, aspect ratio and real size. Advanced adds viewing distance, scaling, print size and a second screen to compare.
Desk monitor about 24 in (60 cm); phone about 12 in (30 cm); TV 6–10 ft (2–3 m).
The zoom set in your computer's display settings. 150% makes everything 1.5× bigger.
Common screens and their PPI
| Screen | Resolution | Size | PPI | Pixels vanish beyond |
|---|---|---|---|---|
| Full HD monitor | 1920 × 1080 | 24 in | 91.8 | 37.5 in (95 cm) |
| Full HD monitor | 1920 × 1080 | 27 in | 81.6 | 42.1 in (107 cm) |
| QHD monitor | 2560 × 1440 | 27 in | 108.8 | 31.6 in (80 cm) |
| QHD monitor | 2560 × 1440 | 32 in | 91.8 | 37.5 in (95 cm) |
| Ultrawide monitor | 3440 × 1440 | 34 in | 109.7 | 31.3 in (80 cm) |
| 4K monitor | 3840 × 2160 | 27 in | 163.2 | 21.1 in (54 cm) |
| 4K monitor | 3840 × 2160 | 32 in | 137.7 | 25.0 in (63 cm) |
| 5K monitor | 5120 × 2880 | 27 in | 217.6 | 15.8 in (40 cm) |
| Laptop | 1920 × 1080 | 15.6 in | 141.2 | 24.3 in (62 cm) |
| High-res laptop | 2880 × 1800 | 15.3 in | 222.0 | 15.5 in (39 cm) |
| Full HD TV | 1920 × 1080 | 55 in | 40.1 | 7.2 ft (2.18 m) |
| 4K TV | 3840 × 2160 | 65 in | 67.8 | 50.7 in (129 cm) |
| 8K TV | 7680 × 4320 | 75 in | 117.5 | 29.3 in (74 cm) |
| Phone | 1170 × 2532 | 6.1 in | 457.3 | 7.5 in (19 cm) |
| Large phone | 1440 × 3200 | 6.8 in | 516.0 | 6.7 in (17 cm) |
How your PPI is worked out
Count the pixels along the diagonal, then share them over the inches.
- 1
Pixels on the diagonal
√(1920² + 1080²)
= 2,202.9 px - 2
Share over the inches
2,202.9 ÷ 24 in
= 91.79 PPI - 3
Gap between pixels
25.4 ÷ 91.79
= 0.277 mm - 4
Where pixels vanish
3,437.7 ÷ 91.79
= 37.5 in
Read more: the formula, a worked example, viewing distance and print sizes
Pixel density tells you how tightly a screen packs its pixels. The more pixels per inch, the smaller each pixel and the sharper text and photos look. Two screens with the same resolution can look very different: a 24 in and a 32 in monitor both at 1920 × 1080 have the same number of pixels, but the bigger one spreads them out.
The formula
pixels on the diagonal = √(width in pixels² + height in pixels²)
PPI = pixels on the diagonal ÷ diagonal in inches
dot pitch (mm) = 25.4 ÷ PPI
screen width = diagonal × width px ÷ diagonal px (height the same way)
pixels per degree = 2 × distance × tan(0.5°) × PPI
pixels vanish beyond = 1 ÷ (PPI × tan(1 arcminute)) = 3,437.7 ÷ PPI inches
largest print = pixels ÷ print DPI
If your size is in centimetres, divide it by 2.54 first to get inches.
Worked example
A 24 in monitor with a 1920 × 1080 resolution. Pixels on the diagonal: √(1920² + 1080²) = √(3,686,400 + 1,166,400) = √4,852,800 = 2,202.9. PPI = 2,202.9 ÷ 24 = 91.79 PPI.
Dot pitch = 25.4 ÷ 91.79 = 0.277 mm. The screen is 24 × 1920 ÷ 2,202.9 = 20.92 in wide (53.1 cm) and 24 × 1080 ÷ 2,202.9 = 11.77 in tall (29.9 cm), an area of 246.1 sq in. It has 1920 × 1080 = 2,073,600 pixels, or 2.07 megapixels, in a 16:9 shape.
From 24 in away, 1° of your view covers 2 × 24 × tan(0.5°) = 0.41889 in, which holds 0.41889 × 91.79 = 38.45 pixels per degree. Pixels vanish beyond 3,437.7 ÷ 91.79 = 37.5 in (95 cm), so at a 24 in desk distance you can still make out single pixels. To make them vanish at 24 in you'd need 3,437.7 ÷ 24 = 143 PPI, which a 27 in 4K monitor (163.18 PPI) beats.
An image of 1920 × 1080 pixels prints at most 1920 ÷ 300 = 6.4 in by 1080 ÷ 300 = 3.6 in at 300 DPI (photo quality), or 12.8 × 7.2 in at 150 DPI (fine for posters seen from further away).
Display scaling
On a high-PPI screen, your computer zooms everything so text isn't tiny. At 150% a 3840 × 2160 screen lays things out like a 2560 × 1440 one (3840 ÷ 1.5 and 2160 ÷ 1.5), but draws them with all its real pixels, so text stays crisp. On a 27 in screen that is 163.18 ÷ 1.5 = 108.8 "looks-like" PPI, about the same size as a 27 in QHD monitor.
Pixel density by device
| Device | Typical PPI | Typical distance |
|---|---|---|
| TV | 30–120 | 6–10 ft (2–3 m) |
| Desktop monitor | 80–220 | 20–30 in (50–75 cm) |
| Laptop | 120–260 | 16–24 in (40–60 cm) |
| Tablet | 220–330 | 12–16 in (30–40 cm) |
| Phone | 300–550 | 10–14 in (25–35 cm) |
The 1-arcminute rule (20/20 vision) is a common guide, not a hard limit: younger or sharper eyes resolve a little finer detail, and smooth-looking text also depends on font rendering. PPI assumes square pixels, which almost every modern screen has. Checked 2026-10-13.
Common questions
How do you work out PPI?
Find the number of pixels along the screen's diagonal with Pythagoras, √(width² + height²), then divide by the diagonal size in inches. A 24 in Full HD (1920 × 1080) monitor has √(1920² + 1080²) = 2,202.9 pixels on the diagonal, and 2,202.9 ÷ 24 = 91.79 PPI.
What is a good PPI?
It depends on how far away you are. At a desk (about 2 ft or 60 cm), around 110 PPI looks fine and 140 PPI or more makes single pixels hard to see. Laptops are often 140–220 PPI and phones 400–500 PPI because they are held closer. TVs are watched from far away, so a 65 in 4K TV at only about 68 PPI still looks sharp from the sofa.
What is the difference between PPI and DPI?
PPI (pixels per inch) is how many pixels a screen or digital image packs into an inch. DPI (dots per inch) is how many ink dots a printer lays down. People often mix them up; when sizing a photo for print, "300 DPI" usually means 300 image pixels per printed inch.
What is dot pitch?
Dot pitch (or pixel pitch) is the distance from the centre of one pixel to the next, usually in millimetres. It is 25.4 ÷ PPI. A 24 in Full HD screen has a dot pitch of 0.277 mm; a 27 in 4K screen 0.156 mm. Smaller means sharper.
At what distance can I no longer see pixels?
A common rule says an eye with 20/20 vision can just tell apart details 1 arcminute (1/60 of a degree) wide. Pixels vanish beyond 3,438 ÷ PPI inches. For a 91.79 PPI monitor that is 37.5 in (95 cm); for 163 PPI it is 21 in (54 cm). Sharp young eyes see a little finer, so treat it as a guide.
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