How do I know the dpi of my laptop screen

My laptop is HP 250 G2 with 15.6” diagonal LED-backlit HD2 anti-glare (1366 x 768). Please How do I know the dpi value?

1366 x 768 pixels is 1567 pixels diagonally (Pythagorean theorem, √(1366²+768²)=1567; and you thought you would never use that).

If the screen measures 15.6" diagonally, 1567 pixels / 15.6" is approximately 100 pixels per inch.

You won't get an exact PPI number unless the manufacturer publishes it or you measure the screen. The advertised diagonal measurement is often a nominal number and may include a little of the display panel behind the bezel.

Assuming you are using Windows 7:

• Go to Control Panel > Appearance and Personalization > Display
• In the left(blue) column, click Set custom text size(DPI)

A window titled Custom DPI Scaling will pop up. It will show what percent of the "normal size"(default monitor DPI) it is scaled to and will allow you to adjust it.

You should see a ruler in the middle. Below that it will say 9 point Segoe UI at X pixels per inch.

The X is your current DPI.

Try yourself: DPI Calculator

Formula:

PPI = √(pixels_horizontal^2 + pixels_vertical^2) / inches_diagonal

PPI = √(1366² + 768²) / 15.6 = 100.45

Therefore, 100.45 dpi