To check screen resolution in a browser, open a page that reads the standard window and screen objects your browser already exposes, and it will display the full CSS screen width and height, the available screen area, the current viewport, the outer browser window, and the device pixel ratio — plus the labelled estimate of backing-store pixels calculated as round(CSS screen × devicePixelRatio). On a typical 1440 × 900 CSS screen at devicePixelRatio 2, the estimate lands at 2880 × 1800, which is the common Retina-style mapping between CSS coordinates and the panel's addressable pixel store. These are the values a webpage can actually read — they describe the coordinate space that web content sees, not the inches, dot pitch, or colour depth of the physical panel. Resizing the browser window, changing zoom, switching displays, entering fullscreen, or moving the window between monitors can all change what gets reported, so the same page can show different numbers from one visit to the next.
What your browser actually exposes about the display
A webpage running in your browser has access to a small set of well-defined properties that describe the coordinate environment around it. These come from the standard window and screen JavaScript objects, and they are the only display-related numbers a normal web page can read.
The full CSS screen dimensions come from screen.width and screen.height. They describe the coordinate space that the browser exposes to web content — not necessarily the panel's marketed or native resolution. The available screen dimensions come from screen.availWidth and screen.availHeight, and may exclude operating-system interface areas such as a taskbar or menu region.
The viewport dimensions come from window.innerWidth and window.innerHeight: the area available to the page's layout viewport, including any space defined by browser behaviour. The outer window values come from window.outerWidth and window.outerHeight, when the browser provides positive values. The difference between outer and inner dimensions can include browser chrome, borders, side panels, developer tools, and platform-specific decorations.
The browser also reports a devicePixelRatio. Multiplying a CSS dimension by this ratio gives a rough estimate of the backing-store pixel grid, but the ratio itself is influenced by browser zoom, operating-system scaling, compositor behaviour, and display configuration. The Screen Resolution Checker reads all of these values locally and presents them with explicit labels so the reader can tell them apart at a glance.
How to read the dimensions with Screen Resolution Checker
- Open the Screen Resolution Checker in any modern browser.
- Compare the four labelled dimension groups: CSS screen, available screen, viewport, and outer browser window.
- Review the device pixel ratio and the clearly labelled estimate of backing-store pixels, remembering the estimate is not a physical measurement.
- Resize the browser window, change zoom, switch displays, or enter fullscreen when you want to compare conditions.
- Select Copy report to place every visible field as plain text on the clipboard, ready to paste into a note, ticket, or chat.
Understanding the numbers on the page
Each row on the report answers a different question. Reading them together gives you a complete picture of the coordinate environment a webpage sees at this moment.
| Field | Source | What it describes |
|---|---|---|
| CSS screen width / height | screen.width, screen.height | Full coordinate space exposed to web content, in CSS pixels. |
| Available screen width / height | screen.availWidth, screen.availHeight | Screen area after OS interface regions such as the taskbar are excluded. |
| Viewport width / height | window.innerWidth, window.innerHeight | Layout area inside the browser chrome. |
| Outer window width / height | window.outerWidth, window.outerHeight | Entire browser window including chrome, borders, and side panels. |
| Device pixel ratio | window.devicePixelRatio | Browser's reported scaling factor for this view. |
| Estimated device pixels | round(CSS screen × ratio) | Labelled estimate of the backing-store grid. |
| Orientation | Comparison of CSS width vs height | Landscape, Portrait, or Square — based on the two reported numbers only. |
The estimated device-pixel multiplication is deliberately labelled. On a 1440 × 900 CSS screen with a devicePixelRatio of 2, the calculation is 1440 × 2 = 2880 and 900 × 2 = 1800, giving an estimate of 2880 × 1800 backing-store pixels. That figure describes the relationship between CSS coordinates and the backing store, not the physical panel's native addressable pixels — display scaling, browser zoom, operating-system scaling, compositor behaviour, screenshots, remote desktops, multi-panel arrangements, and privacy reduction can all prevent the multiplication from matching the panel's actual pixel count.
Why the numbers change between sessions
Because the values come from the live browser environment, anything that changes that environment changes what gets reported. The widget refreshes on window resize, so moving or resizing the browser updates the viewport and outer window values immediately. Browser zoom, operating-system scaling, the presence of side panels or developer tools, and entering or leaving fullscreen mode all change the layout viewport while leaving the full CSS screen dimensions untouched.
Available screen dimensions shift when the operating system shows or hides interface elements like a taskbar or menu region. Moving the window to a different display in a multi-monitor setup, or connecting to a remote session, can change the full CSS screen dimensions because the coordinate space that web content sees changes with the panel. Privacy behaviours in some browsers intentionally reduce the precision of reported values.
For a useful troubleshooting report, copy the values before and after changing browser zoom, moving the window to another display, entering fullscreen, or changing operating-system scaling. Record the conditions outside the page because the widget intentionally saves no history. A change between two snapshots shows that the coordinate environment changed; it does not by itself identify which layer caused the change.
What Screen Resolution Checker cannot measure
The report only describes what the browser's standard window and screen objects expose. It cannot measure inches, centimetres, dots per inch, pixel pitch, colour depth, refresh rate, HDR support, gamut, brightness, panel type, physical diagonal, cable capability, GPU output mode, or EDID data. A normal web page does not receive enough trustworthy hardware information for those claims, so the widget stays within the narrow contract of validating positive finite browser values, calculating an openly described multiplication, updating on window resize, and distinguishing CSS coordinates from estimated device pixels and from unobservable physical size.
Use operating-system display settings, manufacturer specifications, or dedicated hardware tools when purchasing, diagnosing, or calibrating a display. All values on the page are read locally from the standard window and screen objects. No display identifier, report, clipboard content, or dimensions are uploaded or stored after reload.