By Ahsan Khowaja · Updated 27 October 2026
How to use the PPI calculator
- Type the screen's resolution: the horizontal and vertical pixel counts, such as 1920 and 1080. You'll find them in the display settings of your computer or phone, or on the product's spec sheet.
- Type the diagonal size in inches or centimetres. This is the advertised size (24-inch, 55-inch), measured corner to corner across the picture, not the frame.
- Read the pixel density in PPI, the dot pitch in millimetres, the pixels per centimetre, the total pixel count and the screen's physical width and height.
The pixel density calculator also lists the same resolution at other common diagonals, so you can see at a glance whether a 27-inch or a 32-inch panel suits the resolution you're considering.
The pixels per inch formula
PPI stands for pixels per inch: how many pixels fit along one inch of the screen. Because a screen is sold by its diagonal, you first need the diagonal in pixels, which Pythagoras gives you:
- Diagonal pixels = √(width² + height²)
- PPI = diagonal pixels ÷ diagonal inches
For a 24-inch 1920 × 1080 monitor: √(1920² + 1080²) = √4,852,800 = 2,202.9 pixels along the diagonal. Divide by 24 inches and you get 91.8 PPI. Each pixel is therefore 1 ÷ 91.8 = 0.0109 inches wide, or 0.277 mm; that distance from one pixel centre to the next is the dot pitch.
This pixels per inch calculator works on any rectangular display, from a smartwatch to a cinema screen, as long as the pixels are square (they are on virtually every modern screen). Because the aspect ratio is already in the pixel counts, you don't have to enter it separately.
PPI of common screens
Each value below was calculated with the formula above from the stated resolution and diagonal.
| Screen | Resolution | Diagonal | PPI | Dot pitch |
|---|---|---|---|---|
| Laptop (HD) | 1366 × 768 | 15.6 in | 100.5 | 0.253 mm |
| Laptop (Full HD) | 1920 × 1080 | 15.6 in | 141.2 | 0.180 mm |
| Laptop (high density) | 2560 × 1600 | 13.3 in | 227.0 | 0.112 mm |
| Monitor (1080p) | 1920 × 1080 | 24 in | 91.8 | 0.277 mm |
| Monitor (1080p) | 1920 × 1080 | 27 in | 81.6 | 0.311 mm |
| Monitor (1440p) | 2560 × 1440 | 27 in | 108.8 | 0.233 mm |
| Monitor (1440p) | 2560 × 1440 | 32 in | 91.8 | 0.277 mm |
| Ultrawide | 3440 × 1440 | 34 in | 109.7 | 0.232 mm |
| Monitor (4K) | 3840 × 2160 | 27 in | 163.2 | 0.156 mm |
| Monitor (4K) | 3840 × 2160 | 32 in | 137.7 | 0.184 mm |
| TV (4K) | 3840 × 2160 | 55 in | 80.1 | 0.317 mm |
| TV (4K) | 3840 × 2160 | 65 in | 67.8 | 0.375 mm |
Two things stand out. A 27-inch 1080p monitor and a 32-inch 1440p monitor have the same pixel density as a 24-inch 1080p screen (about 92 PPI), so text looks the same size and sharpness on all three; you just get more of it on the larger panels. And a 65-inch 4K TV has a lower monitor PPI figure than a cheap laptop, which is fine because you sit several metres from it.
PPI calculator for 4K screens
4K UHD is 3840 × 2160, so the diagonal is always 4,405.8 pixels. Divide by the size:
- 27 in → 163.2 PPI (very sharp; Windows and macOS normally scale the interface to 150% or 200%)
- 32 in → 137.7 PPI (sharp, usually run at 125% or 150% scaling)
- 43 in → 102.5 PPI (close to a standard desktop monitor, often used at 100%)
- 55 in → 80.1 PPI, 65 in → 67.8 PPI, 75 in → 58.7 PPI (TVs, viewed from a distance)
Whether 4K looks sharper than 1440p on your desk depends on the viewing distance as well as the PPI. The TV viewing distance calculator works out how far away you need to sit before the extra pixels stop being visible.
Dot pitch and pixels per centimetre
Dot pitch is the inverse of PPI: dot pitch (mm) = 25.4 ÷ PPI. Monitor makers often quote it instead of PPI. A 0.277 mm pitch means 91.8 PPI; a 0.233 mm pitch means 108.8 PPI. Smaller is sharper.
Outside the US, screens are sometimes described in pixels per centimetre (px/cm): px/cm = PPI ÷ 2.54. The 24-inch 1080p monitor is 36.1 px/cm. The calculator shows both.
Phone screens and the iPhone PPI
Phones have far higher densities than monitors because you hold them 30 cm from your eyes. You can check a maker's quoted figure with this pixel density calculator: Apple lists the iPhone 15 as a 6.1-inch display with 2556 × 1179 pixels at 460 ppi. Putting 2556, 1179 and 6.1 into the calculator gives 461.4 PPI. The small gap is the rounded diagonal: Apple's footnote gives the screen's full rectangle as 6.12 inches, and 2,814.8 ÷ 6.12 = 459.9, which rounds to the quoted 460. Expect the same ±1% wobble for any phone, because advertised sizes are rounded and curved corners trim the real diagonal.
Apple's original "Retina display" claim, made for the 326 PPI iPhone 4 in 2010, was that at a normal phone viewing distance of about 10 to 12 inches the eye can no longer pick out individual pixels at roughly 300 PPI. The idea generalises: the further away a screen is, the fewer pixels per inch it needs to look smooth. That's why a 218 PPI laptop and an 80 PPI TV can both count as "retina" at their intended distances.
Screen PPI vs print PPI (and DPI)
Searches for a ppi calculator for printing are really about a different number. For a screen, PPI is a physical property of the hardware: the pixels are already spaced a fixed distance apart. For a print, PPI (or DPI, which print software uses to mean the same thing) is a choice you make when you decide how large to print an image. A 3000 × 2000 photo has no PPI on its own; print it 10 inches wide and it becomes 300 PPI, print it 20 inches wide and it drops to 150 PPI.
So for printing, use the DPI calculator, which turns pixels and a print size into a resolution, or the print size calculator to find the biggest print an image supports at 300 DPI. Our guide to what DPI means covers the "72 DPI vs 300 DPI" confusion in more depth.
How many PPI do you need?
There is no single right answer because viewing distance matters as much as density, but these ranges match how screens are actually used:
- Desktop monitors at 100% scaling: roughly 90 to 110 PPI. Text set at 100% looks the size most people expect. Above about 120 PPI you'll want operating-system scaling, which some older apps handle badly.
- "Retina" style monitors: 160 to 220 PPI run at 200% scaling, so everything is the same size as a 90 PPI screen but twice as sharp.
- Laptops: 140 to 230 PPI, almost always with scaling turned on.
- Phones: 300 to 500+ PPI.
- TVs: 40 to 160 PPI depending on size; the right figure depends on the seating distance.
PPI tells you nothing about colour, contrast, brightness or refresh rate, and a sharp screen with a bad panel is still a bad screen. Use it to judge sharpness and interface scaling, then look at the other specs separately.
