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PPI vs DPI: what's the difference, and which one is your screen actually using?

By TechCompare · Updated · How we check

PPI is for screens, and DPI is for printers and mice. When a monitor spec sheet, Windows scaling slider, or Photoshop dialog mentions DPI for a screen, it means PPI. Use the PPI calculator to get the real pixel density of any display.

Same 40 × 20 mm of Screen, at Real Pixel Density

This simulation shows an identical 40 × 20 mm (1.57 × 0.79 inch) physical patch magnified at native pixel resolution. It demonstrates how typography and curves render across different screen densities.

Standard 24-inch 1080p92 PPI · 145×72 px

Standard desktop baseline with noticeable pixel staircasing on fine text.

27-inch 1440p109 PPI · 171×86 px

Crisp for desk work. Pixel structure is faint unless viewed very closely.

Diagonal physical size: 27 inches (68.6 cm)
Native resolution: 2560 × 1440
This exact 2560×1440 at 27″ panel, pre-loaded. Compare another size or try a second panel.
Edit in the full tool

PPI (pixels per inch) and DPI (dots per inch) get used interchangeably all the time, and most of the time that's wrong. PPI measures how many physical pixels a screen packs into one inch of display.

DPI measures how many ink dots a printer lays down in one inch of paper, or how many counts a mouse sensor reports per inch of movement. Monitor sharpness is measured in PPI. Printer drivers care about DPI. Your gaming mouse reports DPI too, and the three have almost nothing to do with each other beyond sharing the word 'per inch'.

How this is calculated

PPI is a physical property of a display: take the diagonal pixel count (sqrt(width² + height²)) and divide by the diagonal size in inches. A 27-inch 1440p monitor has sqrt(2560² + 1440²) ≈ 2937 pixels across 27 inches, so 109 PPI.

Bump the resolution to 4K on the same 27-inch panel and the PPI jumps to 163. The math is unambiguous and the number doesn't change unless you physically change the panel.

DPI for printers describes how many discrete ink dots a printer places per inch. A 600 DPI laser printer lays down 600 dots per inch, a 1200 DPI photo printer lays down 1200. Higher DPI generally means finer detail, but the relationship isn't 1-to-1 with image resolution because multiple dots can blend to form a single pixel of color. Designers working for print care about DPI. Designers and shoppers working for screens care about PPI.

The third, unrelated DPI is the one gaming mice report. Mouse DPI (also called CPI, counts per inch) is how many sensor counts the mouse emits per inch of physical movement. A 1600 DPI mouse moved one inch sends 1600 counts to the computer. Higher DPI doesn't mean more accuracy, it means more counts for the same motion, which you then scale in software. Many competitive players run 400-1600 DPI and adjust sensitivity separately.

The reason the confusion persists is historical: Windows calls its display scaling 'DPI scaling' even though it's regulating PPI-equivalent logical sizes, and Photoshop still labels its image resolution field 'Resolution: Pixels/Inch' inside a dialog titled 'DPI'. When someone asks 'what's the DPI of this monitor', they almost always mean PPI. The answer below uses PPI throughout for screens and reserves DPI for printers and mice.

Verdict

Use PPI for anything on a screen, and DPI only for printers and mouse sensors. PPI is a physical display property: take the diagonal pixel count (sqrt(width² + height²)) and divide by the diagonal size in inches, e.g. a 27-inch 1440p panel hits sqrt(2560² + 1440²) / 27 ≈ 109 PPI.

DPI for printers is a separate property of ink on paper, and the gaming-mouse DPI (also called CPI) is a sensor count per inch of movement, where higher means more counts for the same motion rather than more accuracy. The confusion persists because Windows calls its display scaling 'DPI scaling' and Photoshop labels its image resolution field 'Resolution: Pixels/Inch' inside a dialog titled 'DPI', and both describe PPI under a mislabeled heading.

More Concepts scenarios

24" 1080p monitor
A 24-inch 1080p monitor works out to 91.79 PPI, the baseline pixel density most people grew up with and the point where standard sub-pixel font rendering still looks crisp at a typical desk distance.
View details
24" 1440p monitor
A 24-inch 1440p monitor delivers 122.38 PPI, a high density for a desktop panel.
View details
27" 1080p monitor
A 27-inch 1080p monitor works out to 81.59 PPI, a low pixel density that gives the same 1920×1080 grid larger physical pixels than on a smaller panel.
View details

Related guides

24" 16:9 monitor screen size
The reference 24-inch monitor size where 91.79 PPI is computed.
View guide
Flat 27" 16:9 monitor curve
A flat 27-inch panel as a PPI baseline reference.
View guide

Frequently asked questions

Is PPI the same as DPI?
No. PPI (pixels per inch) measures how many physical pixels a screen packs into one inch of display. DPI (dots per inch) measures how many ink dots a printer lays down per inch, or how many counts a mouse sensor reports per inch. They share the word 'per inch' but describe completely different things.
Why does Windows call display scaling 'DPI scaling'?
Historical naming. When Windows adopted logical pixel scaling in the mid-2000s, the language it used was 'DPI awareness' and 'DPI scaling' even though what's actually being regulated is PPI-equivalent logical sizes. The label stuck and now confuses everyone. The setting affects how large UI elements appear given your screen's physical PPI.
What DPI should I use for printing?
300 DPI is the standard for photographic print quality on paper. 150 DPI is acceptable for large format posters viewed at distance. 600 DPI or higher is normal for text and line art on laser printers. DPI for print is a property of the printer or the exported image file, completely separate from your monitor's PPI.
Does higher mouse DPI mean better accuracy?
No. Mouse DPI (more accurately CPI, counts per inch) is how many sensor counts the mouse emits per inch of physical movement. Higher DPI just means more counts for the same motion, which you then scale in software. Many competitive FPS players run 400-1600 DPI and adjust sensitivity in-game. Native sensor accuracy is what matters, not the DPI number on the box.
What's the PPI of a 24-inch 1080p monitor?
sqrt(1920² + 1080²) ÷ 24 = 91.79 PPI. That's a common desktop monitor density and a handy baseline for comparison. Sit closer than about 95 cm (37 inches)37 inches (95 cm) and you can faintly see pixels. Sit farther and the screen reads as crisp.

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