Why is the viewport smaller than the screen?

The viewport is the page layout area inside the browser. Browser controls, window size, side panels, developer tools, and operating-system regions can make it smaller.

Are estimated device pixels the monitor's native resolution?

Not necessarily. Multiplying CSS dimensions by devicePixelRatio can differ from native panel pixels because of scaling, zoom, privacy reduction, compositing, or remote display behavior.

Can this measure physical screen size or DPI?

No. Browser dimensions do not provide a calibrated ruler, physical diagonal, pixel pitch, or trustworthy hardware DPI.

What does the Landscape, Portrait, or Square label mean?

It compares the two reported CSS screen dimensions. The label is only a numerical classification and does not prove the physical arrangement of the display setup.

Does the checker upload or save my report?

No. Values are read locally from standard window and screen objects. No display identifier, report, clipboard content, or dimensions are uploaded or stored after reload; Copy report places the visible fields in plain text on the clipboard.

What Is My Screen Resolution? Check Screen and Viewport

Your screen resolution as reported by a browser is the width × height of the CSS coordinate space exposed to web content, while the viewport is the area available to the page's layout. A browser can expose several related but different measurements: full screen dimensions, available screen area, viewport dimensions, outer browser-window dimensions, and a device pixel ratio. The Screen Resolution Checker reads those values from the browser, labels each one, and gives you a plain-text report you can copy. This answers the practical question “what is my screen resolution?” for the browser and display arrangement active at that moment. It does not guarantee the physical panel's marketed or native addressable resolution. Browser zoom, operating-system scaling, privacy behavior, window mode, remote sessions, and multiple-display placement can affect what the browser exposes, so a reported value should be understood as browser-reported rather than a measurement of the hardware itself. For web designers, developers, and troubleshooting tasks, it provides a concrete baseline for the coordinate environment a website receives.

What the checker measures

Each field answers a different question. “Screen,” “window,” and “viewport” are often treated as interchangeable, but browsers expose them separately, and each value has a specific purpose.

Reading	Browser value	What it represents	Best use
CSS screen dimensions	screen.width × screen.height	The full CSS coordinate space exposed to web content	Finding the browser-reported screen resolution
Available screen area	screen.availWidth × screen.availHeight	The exposed screen area, which may exclude taskbar or menu regions	Estimating usable desktop space
Viewport	window.innerWidth × window.innerHeight	The layout viewport available to the current page	Checking page layout and responsive-design behavior
Outer browser window	window.outerWidth × window.outerHeight	The browser window's outer dimensions when positive values are available	Checking the total window size
Device pixel ratio	devicePixelRatio	The browser's CSS-to-device-pixel scaling ratio	Understanding how the browser maps CSS coordinates
Estimated device pixels	Rounded CSS screen dimensions multiplied by the ratio	An estimate of backing-store pixel dimensions	Examining the scaling relationship
Orientation	Comparison of CSS screen width and height	Landscape, Portrait, or Square	Quickly classifying the two reported numbers

Only positive, finite browser values are used. If the browser does not provide a positive outer-window dimension, the checker falls back to the viewport for that reading. The orientation label is numerical too: it does not read an accelerometer or reveal how several physical monitors are arranged.

Check your resolution in three steps

Open the checker and compare the four dimension groups. Look at CSS screen width and height first, then compare available screen area, the current viewport, and the outer browser window. Use the full CSS screen pair when someone asks for the screen resolution reported by the browser; use the viewport when the question concerns the space available to a webpage.
Review the device pixel ratio and estimated device-pixel dimensions. Check the clearly labeled ratio and multiplication rather than treating the estimated result as a physical measurement. The estimate helps explain the relationship between CSS coordinates and a possible backing store, but it is not proof of the panel's native addressable resolution.
Resize or move the browser when comparing conditions, then select Copy report. Resizing refreshes the viewport and outer-window readings, while moving the window can reveal whether the browser exposes different values on another display. Select Copy report to place the visible fields in plain text on the clipboard.

Copying a baseline is useful before changing browser zoom, moving to another display, entering fullscreen, or adjusting operating-system scaling. The checker intentionally keeps no reading history, so retain the copied report and write down the condition that produced it outside the page.

Choose the value that matches your question

The most direct answer to “what is my screen resolution?” is the CSS screen width × CSS screen height pair. That is the resolution of the coordinate space the browser exposes to the current page. It should not be automatically relabeled as the monitor's physical or native resolution.

Need the general browser-reported screen dimensions? Use the full CSS screen width × height. These values describe the browser's screen coordinate space.
Testing how much content fits on the page? Use the viewport dimensions. Browser controls, side panels, developer tools, and platform-specific decorations can make the viewport smaller than either screen measurement.
Checking space left after operating-system controls? Use the available screen area. It may exclude areas occupied by a taskbar or menu region.
Measuring the browser window itself? Use the outer-window values. The difference between outer and inner dimensions can include browser chrome, borders, side panels, developer tools, and other platform-specific features.

This distinction prevents a common error: treating the largest reported pair as the resolution of everything visible on the display. The checker deliberately labels these measurements so the number used in a report, support request, or layout test matches the question being answered.

Read pixel ratio and estimated device pixels

The device pixel ratio describes how many device pixels the browser associates with each CSS pixel in its current coordinate environment. The checker multiplies the CSS screen dimensions by that ratio and rounds the results to whole pixels. The output is intentionally labeled “estimated” because the calculation describes a browser-level relationship, not a direct inspection of the display panel.

Formula: rounded CSS screen width × devicePixelRatio gives the estimated device-pixel width; the same calculation applies to height.

For example, with 1440 × 900 CSS screen dimensions and a devicePixelRatio of 2, the width estimate is round(1440 × 2) = 2880 and the height estimate is round(900 × 2) = 1800, producing estimated device-pixel dimensions of 2880 × 1800.

Even that precise calculation may differ from a physical panel's native addressable pixels. Display scaling, browser zoom, operating-system scaling, compositor behavior, screenshots, remote desktops, multiple panels, and privacy reduction can all alter the relationship. Use the estimate to understand the reported scaling context, not to declare the panel's exact hardware specification.

Orientation is a classification, not a hardware diagnosis

The checker compares the reported CSS screen width and height. A greater width is labeled Landscape, a greater height is labeled Portrait, and equal values are labeled Square. This does not lock device orientation, detect an accelerometer, or prove whether a hinged, folded, rotated, mirrored, projected, or multi-monitor setup is physically arranged in a particular way.

Compare readings after changing conditions

A single report answers what the browser exposes now. A comparison reveals whether its reported coordinate environment changes under different conditions.

Establish a baseline: Copy the visible report before changing anything.
Resize the browser: Watch the viewport and outer-window values refresh after the window changes size.
Move the window: Repeat the check on another display if the browser exposes different screen information for that placement.
Change scaling or browser mode: Compare readings before and after changing browser zoom, operating-system scaling, or fullscreen state.
Save each result: Select Copy report again and label the copied text with the condition you tested.

A changed value shows that the browser's coordinate environment changed; it does not identify which layer caused the change. Browser behavior, operating-system configuration, window mode, privacy settings, remote sessions, and multi-display placement can all participate, so the copied report and external notes are more useful than a single unexplained number.

Know when browser readings are not enough

The tool cannot measure physical display specifications that an ordinary web page does not receive reliably. It does not report:

Physical diagonal size, dimensions in inches or centimeters, pixel pitch, or trustworthy hardware DPI;
Color depth, refresh rate, HDR support, gamut, brightness, or panel type;
Cable capability, GPU output mode, or EDID data.

It also cannot guarantee native panel resolution from browser CSS values. For purchasing decisions, display diagnosis, or calibration, use operating-system display settings, manufacturer specifications, or dedicated hardware tools. For browser layout, scaling behavior, and coordinate troubleshooting, the Screen Resolution Checker provides the relevant browser-level readings in one labeled report.