PPI Calculator
Enter your screen's diagonal size and resolution to find its exact pixel density (PPI). Use this to calibrate your online ruler for accurate measurements.
Common Screen PPI Reference
| Screen | Diagonal | Resolution | PPI |
|---|---|---|---|
| 13" MacBook Air M2 | 13.6" | 2560×1664 | 224 |
| 14" MacBook Pro M3 | 14.2" | 3024×1964 | 254 |
| 15.6" Laptop (HD) | 15.6" | 1920×1080 | 141 |
| 24" Monitor (FHD) | 23.8" | 1920×1080 | 93 |
| 27" Monitor (QHD) | 27.0" | 2560×1440 | 109 |
| 27" 4K Monitor | 27.0" | 3840×2160 | 163 |
| iPhone 15 | 6.1" | 2556×1179 | 460 |
| iPhone 15 Pro Max | 6.7" | 2796×1290 | 460 |
| iPad Air 11" | 11.0" | 2360×1640 | 264 |
| Samsung Galaxy S24 | 6.2" | 2340×1080 | 416 |
Frequently Asked Questions
What is PPI?
PPI stands for Pixels Per Inch — the number of pixels packed into one inch of your screen. A higher PPI means a sharper, crisper display. Most monitors are 90–120 PPI; laptops are 140–220 PPI; phones are 300–460 PPI.
How do I find my monitor's PPI?
Enter your screen's diagonal size (printed on the box or in system settings) and its resolution (width × height in pixels) into the calculator above. The formula is: PPI = √(width² + height²) ÷ diagonal inches.
Why does PPI matter for an online ruler?
An online ruler needs to know your PPI to draw measurements at the correct physical size. Without calibration, the ruler assumes 96 PPI — which is wrong for most modern screens. A 15" laptop at 96 PPI assumption makes 1 cm appear 40% too large.
What is a good PPI for a monitor?
For a desktop monitor viewed at ~60 cm, 100–110 PPI looks sharp. Laptops at 200+ PPI are noticeably crisper. Anything below 90 PPI on a monitor you sit close to will show visible pixels.
Is DPI the same as PPI?
Not exactly. PPI (Pixels Per Inch) refers to screen density. DPI (Dots Per Inch) refers to print resolution. They are often used interchangeably in casual conversation, but for screens, PPI is the technically correct term.
How many pixels is 1 cm on my screen?
It depends on your PPI. At 96 PPI: 1 cm ≈ 37.8 px. At 144 PPI: 1 cm ≈ 56.7 px. At 220 PPI: 1 cm ≈ 86.6 px. Formula: pixels per cm = PPI ÷ 2.54.