PPI Calculator
Calculate your screen's pixel density from its resolution and physical diagonal size. Width and height are auto-filled from your device — enter the diagonal in inches and press Calculate.
Results
Enter your screen details and press Calculate to see PPI, dot pitch, display size, and more.
What does this PPI calculator do?
This free PPI calculator works out your screen's pixel density — the number of pixels per inch (PPI) — from its resolution and physical diagonal size. Alongside PPI it shows dot pitch, the physical display width and height, the aspect ratio, and total megapixels, giving you a full picture of how sharp a display is.
How to calculate PPI (with example)
Pixel density is the diagonal resolution in pixels divided by the diagonal size in inches:
PPI = Diagonal (pixels) ÷ Diagonal (inches)
Diagonal (pixels) = √(width² + height²)
Example. Find the PPI of a 27-inch monitor at 2560 × 1440.
Step 1 — diagonal in pixels:
√(2560² + 1440²) = √(6,553,600 + 2,073,600) = √8,627,200 ≈ 2937.2 px
Step 2 — divide by the 27-inch diagonal:
2937.2 ÷ 27 ≈ 108.8 PPI
How to calculate dot pitch (DPI)
Dot pitch is the physical distance between neighboring pixels, in millimeters. It's the inverse of pixel density, converted from inches to millimeters:
Dot pitch (mm) = (Diagonal inches ÷ Diagonal pixels) × 25.4
For the 27-inch example above: (27 ÷ 2937.2) × 25.4 ≈ 0.233 mm. A smaller dot pitch means a higher PPI and a sharper image.
PPI vs. DPI
PPI (pixels per inch) describes screens, while DPI (dots per inch) properly describes printers — but the terms are often used interchangeably for displays, so this also works as a DPI calculator for finding your monitor or phone's pixel density.
Use your PPI to calibrate the ruler
Knowing your exact pixel density is what makes on-screen measuring accurate. After calculating, save the value and open the online ruler already calibrated to your display, or download a printable ruler if you'd rather measure on paper.
Frequently asked questions
What is PPI and why does it matter?+
PPI (pixels per inch) describes how many pixels your display packs into one inch. The ruler converts pixels to centimeters and inches using your PPI, so getting it right is what makes measurements accurate.
How do I find my screen's diagonal size?+
It's the manufacturer's advertised size — the distance corner to corner across the display, in inches (for example, a 27-inch monitor or a 13.3-inch laptop). Check the spec sheet or product listing if you're unsure.
What is dot pitch?+
Dot pitch is the physical distance between pixels, here shown in millimeters. A smaller dot pitch means a sharper, denser display.
Can I use the calculated PPI in the ruler?+
Yes. After calculating, press "Use this PPI for ruler" to save it and open the online ruler already calibrated to your screen.