PPI Calculator: Find Your Screen’s Pixels Per Inch
Enter your screen resolution and size to get its PPI in seconds. Use the result to calibrate the mm ruler, or to compare screens.
Calculate your screen’s PPI
Type your screen’s native resolution and size, or press Detect my screen for the resolution.
Detected on this device: –. If your computer uses display scaling, the detected size may differ from your native resolution.
How to Calculate PPI (Pixels Per Inch)
PPI is the diagonal resolution divided by the diagonal screen size.
- Formula: PPI = square root of (width² + height²) / diagonal in inches.
- Example: a 15.6 inch screen at 1920 x 1080 has a diagonal of about 2203 pixels, so PPI = 2203 / 15.6 = 141.2.
- Pixel size: 25.4 mm divided by PPI. At 141.2 PPI each pixel is about 0.18 mm.
Screen PPI Chart for Common Sizes
Typical monitor and laptop sizes worked out with the formula above. Real screens vary slightly because sizes are rounded.
| Screen size | Resolution | PPI | Pixel size (mm) |
|---|---|---|---|
| 13.3″ | 1920 x 1080 | 165.6 | 0.153 |
| 15.6″ | 1920 x 1080 | 141.2 | 0.180 |
| 24″ | 1920 x 1080 | 91.8 | 0.277 |
| 27″ | 2560 x 1440 | 108.8 | 0.233 |
| 27″ | 3840 x 2160 | 163.2 | 0.156 |
| 32″ | 3840 x 2160 | 137.7 | 0.184 |
Use Your PPI to Calibrate the MM Ruler
The mm ruler online shows true millimeters when it knows your screen’s PPI. Calculate it here, press Use for the mm ruler, then open the ruler. You can also calibrate with a credit card on the ruler page if you do not know your screen size. Prefer paper? Download the free printable mm ruler.
PPI Calculator: Frequently Asked Questions
What is PPI?
PPI means pixels per inch. It tells you how many pixels fit in one inch of a screen. A higher PPI means a sharper image and smaller pixels.
How do I calculate PPI?
Divide the diagonal resolution in pixels by the diagonal screen size in inches. The diagonal resolution is the square root of (width squared plus height squared). For a 15.6 inch 1920 x 1080 screen that is about 2203 / 15.6 = 141 PPI.
What is the difference between PPI and DPI?
PPI describes the pixels on a screen. DPI describes the dots of ink a printer places per inch. The two are often confused, but they measure different things.
How do I find my screen’s resolution?
On Windows open Settings, then System, then Display. On a Mac open System Settings, then Displays. The calculator also fills in your detected resolution when you press the detect button.
What PPI should I use to calibrate the online ruler?
Use the physical PPI that this calculator gives from your screen’s native resolution and its diagonal size. Then press Use for the mm ruler to save it in your browser.
Why does my PPI look wrong?
Display scaling can change the resolution a browser reports. If the numbers look off, type your screen’s native resolution from your display settings instead of the detected one.
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