What the numbers mean
- Screen resolution is the size of your display in CSS pixels, the unit web pages use. With display scaling on, it's smaller than the real resolution.
- Device pixel ratio is how many physical pixels make up one CSS pixel in each direction.
- Estimated native resolution is the screen resolution multiplied by the pixel ratio. On most setups it's the real resolution of your display.
- Aspect ratio is width to height, reduced to the smallest whole numbers. When it's close to a common ratio like 16:9, that's shown too.
- Browser window is the whole window, including tabs, the address bar and borders.
- Viewport is the area inside the window where the page appears. Responsive websites change their layout based on this size.
- Available screen is the screen minus space taken by the taskbar, dock or menu bar.
- Color depth is the number of bits the browser uses per pixel, usually 24 (8 bits each for red, green and blue).
How it works
The tool reads values your browser already exposes to every web page: screen.width andscreen.height, window.devicePixelRatio, the window and viewport sizes, andscreen.colorDepth. It reads them again whenever you resize the window, rotate your device or move to a screen with a different pixel ratio. Nothing is sent anywhere.
The native resolution is an estimate, worked out as screen resolution × pixel ratio. If a Mac reports 1440 × 900 with a ratio of 2, the estimate is 2880 × 1800. With a scaled setting such as "More Space" on macOS, the estimate is the resolution the system draws at, which it then scales to fit the panel. Browser zoom also changes the numbers, so reset zoom to 100% first.
How display scaling changes the reported resolution
| Display resolution | Scaling | Pixel ratio | Resolution the browser reports |
|---|---|---|---|
| 1920 × 1080 | 100% | 1 | 1920 × 1080 |
| 1920 × 1080 | 125% | 1.25 | 1536 × 864 |
| 1920 × 1080 | 150% | 1.5 | 1280 × 720 |
| 2560 × 1440 | 125% | 1.25 | 2048 × 1152 |
| 2880 × 1800 | 200% | 2 | 1440 × 900 |
| 3840 × 2160 | 150% | 1.5 | 2560 × 1440 |
| 3840 × 2160 | 200% | 2 | 1920 × 1080 |
How to find your screen size in inches
Browsers can't measure your screen, so no website can tell you its physical size. Measure the visible screen diagonally from one corner to the opposite corner, without the frame, or look up the model's specifications. Then enter the diagonal and your native resolution in the PPI calculator to get the width, height and pixel density.
To check the display itself, run the dead pixel test or theFPS test to see your refresh rate.