System
Quickly check your screen resolution, viewport size, and display dimensions — all from your browser.
Screen Resolution
screen resolution, display resolution, my screen size
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Open Tool →Device Health
device health, device health check, hardware test
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Open Tool →System
Quickly check your screen resolution, viewport size, and display dimensions — all from your browser.
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Resolution, Viewport, and Device Pixel Ratio
Three different numbers are all called resolution in everyday use, and confusing them causes most of the disagreement between what a browser reports and what a specification sheet claims. The screen resolution is the number of physical pixels the display can address. The viewport size is the area available to the page, which is smaller because the browser chrome, the taskbar and any docked panels take space. The device pixel ratio describes how many physical pixels correspond to one layout pixel.
The device pixel ratio is the field most often overlooked and the one that explains the stranger reports. On a high-density display the ratio can be two or higher, so a viewport reported as a certain width in layout pixels covers twice as many physical pixels. This is why a screenshot of a high-density screen is physically larger than the reported viewport dimensions, without anything being wrong.
Browser zoom changes the ratio without changing the display. Zooming in increases the size of a layout pixel and therefore reduces the reported viewport width, even though the physical panel has not changed at all. Before concluding that a resolution reading is wrong, confirm the zoom level is at its default, because a zoom setting is remembered per site and per window.
Why Reported Resolution Differs From the Spec Sheet
A display can run below its native resolution, and frequently does. When the operating system is set to a scaled mode, the panel is driven at its native resolution by the hardware but the desktop is rendered at a smaller logical resolution and then upscaled. The browser reports what the desktop provides, which is the scaled figure, not the panel native one.
External displays introduce a second source of difference. A monitor connected over a link that cannot carry the full resolution at the desired refresh rate will negotiate a lower combination, and the negotiation happens silently. The specification sheet describes the panel maximum, while the reported figure describes the current link, which are different quantities that happen to share a unit.
Virtual machines and remote sessions replace the display subsystem entirely. In a remote session the reported resolution describes a virtual framebuffer rather than any physical panel, and it can change while the session is running if the window is resized. This is expected behaviour rather than a fault, and it explains most reports of an impossible resolution.
Using Screen Resolution for Troubleshooting
Resolution is most useful in troubleshooting when it is compared against something. Comparing the reported value with the value selected in display settings tells you whether scaling is being applied. Comparing the viewport with the screen resolution tells you how much of the display the browser chrome is consuming, which is the usual explanation for a layout that breaks only on one machine.
For web development the practical use is verifying breakpoints. A layout that looks correct in a resized desktop window can behave differently on a real device, because the window resize changes the viewport while leaving the device pixel ratio alone, whereas a genuine mobile device changes both. Reading the ratio alongside the viewport is what makes the difference visible.
For support purposes, resolution is one of the fastest ways to confirm a user is describing the machine you think they are. A user reporting a problem on a laptop with an external display will have a different reported resolution depending on which screen the browser window is on, and asking for the reported value resolves the ambiguity immediately.
Limits of Browser-Based Display Detection
A browser cannot read the physical size of a display. It has no access to the diagonal measurement or to the panel model, because that information lives in the display EDID data which is not exposed to web pages. Any site claiming to report your exact monitor size in inches is inferring it from the resolution and a guess at the density, which is why those estimates are frequently wrong.
A browser also cannot enumerate every attached display. It reports the screen the window is currently on, plus a combined screen size in some configurations, but it cannot list the panels that are connected but not in use. Testing on a multi-monitor machine therefore requires moving the browser window to each display in turn rather than expecting a single report to cover all of them.
Colour depth is reported as a bit count rather than as a measured capability, and the value reflects the compositing pipeline rather than the panel. A display capable of a higher bit depth can be driven at a lower one by the cable, the operating system setting or the application. The reported depth is what the browser is working with, which is useful, but it is not a statement about the hardware maximum.
System FAQ
How do I find my screen resolution?
Read it directly from the browser rather than from the display settings, because the browser reports the resolution the page is actually working with. That figure already accounts for operating system scaling, so it is the number that explains why a layout or a screenshot behaves as it does. The display settings panel reports the panel mode, which can legitimately differ.
Why does my browser report a lower resolution than my monitor supports?
Because operating system scaling is being applied, or because the link has negotiated a lower mode. The panel may be running at its native resolution in hardware while the desktop is rendered at a smaller logical size and upscaled. Check the scale setting first, then the cable and port, before concluding anything is wrong with the display itself.
What is the difference between screen resolution and viewport size?
Screen resolution describes the whole display, while the viewport is the part of it available to the page. Browser chrome, the taskbar and any docked developer panels all reduce the viewport without changing the screen. This is why a page that fits a resized window can still overflow on a device with the same nominal resolution.
What is device pixel ratio?
It is the number of physical pixels that correspond to one layout pixel. A ratio of two means each layout pixel is drawn with four physical pixels, which is typical on high-density displays. It explains why a screenshot of a high-density screen is physically larger than the reported viewport, and why images can look soft if they are not supplied at the higher density.
Why does my resolution change when I connect an external monitor?
Because the browser reports the display the window is currently on, and moving the window between displays changes that. Mirroring forces both displays to a common mode, which is usually the lower of the two, so a high-resolution laptop panel can appear to lose resolution when it is mirrored to a lower-resolution projector. Extending rather than mirroring avoids this.
Can a website detect my physical monitor size?
No. The diagonal measurement and the panel model are carried in display identification data that browsers do not expose to web pages. Sites that claim to report a physical size are dividing the reported resolution by an assumed pixel density, which is accurate only when the assumption happens to match, so treat any such figure as an estimate rather than a measurement.
Does checking my screen resolution require any download?
No. The values are read from the browser own screen and window interfaces, which are available to any page without a plugin, an extension or an installation. Nothing is downloaded and nothing is transmitted, because the page needs no network access to read information the browser already holds.