What Is a Screen Resolution Checker?
A screen resolution checker is a tool that reports the exact pixel dimensions of your display, the browser's viewport, the device pixel ratio (how many physical pixels per CSS pixel), color depth, and orientation. These numbers come straight from the browser's window and screen APIs, so they describe exactly what a web page sees about your screen — which is often different from what the OS settings say, especially on HiDPI displays where macOS "Retina" or Windows "Scale 125%" multiplies the effective resolution.
Web developers checking how their site looks across breakpoints, designers ordering wallpapers at the correct dimensions, QA testers reproducing bug-report screen sizes, IT admins documenting employee laptop specs, and anyone troubleshooting a Zoom or display-scaling issue use the tool regularly. The Tooldit screen-resolution checker runs entirely in your browser using JavaScript's window/screen APIs — no data is sent anywhere.
Check Your Screen Resolution in One Glance
This screen resolution checker reads your display straight from the browser and lays out the numbers that actually matter when you design, test, or troubleshoot a site. The big readout up top is your full display size in logical pixels, with its aspect ratio and orientation underneath. Below that, a tidy grid breaks out the viewport, available area, device pixel ratio, color depth, physical pixel count, and orientation, followed by your raw user-agent string. You don't install anything, you don't configure anything — the values are already on screen the moment the page loads.
What Each Value Means
Every metric is pulled from your browser's native window.screen and navigator objects, so what you see is exactly what a web page sees about your device:
- Screen Resolution — the full logical size of your display, shown large with its simplified aspect ratio (such as 16:9) and current orientation.
- Viewport — the live drawable area inside the browser window, which shrinks as you add toolbars, open dev tools, or narrow the window.
- Available — the desktop space left after the OS taskbar or dock is subtracted, so it's usually a little less than the full resolution.
- Pixel Ratio — your device pixel ratio, where anything above 1.00 signals a high-DPI or Retina-class panel.
- Color Depth — bits per pixel, typically 24-bit for standard displays and higher on wide-gamut screens.
- Physical Pixels — your resolution multiplied by the pixel ratio, revealing the true number of dots the panel actually drives.
Why Use This Checker
- Reads locally — every number comes from your own browser; none of your display or user-agent details leave the tab.
- Live updates — resize the window or rotate your phone and the viewport figures refresh on the spot, no reload needed.
- Completely free — no trial, no paywall, and no "unlock the full report" upsell.
- No signup — open the page and the answer is already there; no account or email required.
- Nothing to clean up — there's no watermark, no download, and no cookie trail to chase afterward.
Real-World Uses
- Web designers confirm the viewport width a client's laptop reports before deciding which responsive breakpoint to target.
- QA and support teams ask a user to read off their resolution, pixel ratio, and user agent to reproduce a layout bug that only appears on certain screens.
- Gamers and streamers verify a new monitor is running at its native resolution and refresh-friendly aspect ratio instead of a scaled-down mode.
- Remote workers check the available area on an external display before sizing a presentation or screen-share window.
Screen Resolution Checker vs Other Tools
Versus OS settings (Display in System Settings / Settings) — the OS shows the native panel resolution and scaling factor, which is what the hardware reports. The browser checker shows what web pages see, which is the OS values divided by the scaling factor. For web design, the browser value matters more.
Versus whatismyscreenresolution.com / whatismyviewport.com — both work and show similar data, but are ad-heavy and lack the device-pixel-ratio detail needed for retina-aware design. Tooldit shows the numbers without clutter.
Versus browser DevTools' Device Toolbar — DevTools' Toggle Device Toolbar simulates breakpoints but doesn't tell you the real screen. Tooldit shows actuals; DevTools simulates targets.
Versus running JavaScript in the console — you can type window.innerWidth in the console, but the checker formats every relevant property in one view.
Troubleshooting & Common Issues
- Numbers don't match my display spec — OS scaling is the usual cause. macOS Retina and Windows 125%/150% scaling halve or two-thirds the effective pixels reported to web pages. Multiply by the device pixel ratio to get the physical pixels.
- Viewport size keeps changing on mobile — mobile browsers shrink the viewport when the URL bar is visible and expand when scrolled. For consistent breakpoint testing, scroll the page so the URL bar hides.
- Multi-monitor setup shows one monitor only — the screen API reports the monitor the browser window is currently on. Move the window to another monitor and refresh.
- Available width less than total width — the OS taskbar, dock, or other persistent UI elements reduce the available screen area. That's expected behavior.
- Color depth says 24, but my monitor is 10-bit — browsers usually report 24-bit (sRGB) color regardless of monitor capability. HDR and wide-gamut support is signaled separately via CSS media queries.
- Orientation tab doesn't update — some browsers cache orientation. Force a refresh after rotating the device.
Frequently Asked Questions
+What is the difference between screen resolution and viewport size?
Screen resolution is the full size of your physical display in logical pixels — for example 1920 by 1080. Viewport size is the smaller area inside the browser window where a web page actually renders, after subtracting tabs, toolbars, scrollbars, and any docked dev tools. This checker shows both, plus the available area, so you can see exactly how much room a site has to work with on your setup.
+Why is my pixel ratio not 1.00?
A device pixel ratio above 1.00 means your display is high-DPI, like a Retina MacBook or a 4K monitor running with scaling turned on. A ratio of 2.00 means two physical pixels are used for every CSS pixel. The Physical Pixels readout multiplies your resolution by this ratio to show the true pixel count the panel renders, which is useful when exporting graphics at the correct size.
+Does the screen resolution update when I resize the window?
The reported screen resolution stays the same because it reflects the whole display, not the window. The viewport values, however, update live as you drag the window edge, switch to full screen, or rotate a phone or tablet, because the checker listens for resize and orientation-change events and re-reads the numbers instantly.
+Is my display and browser information sent to a server?
No. Every value on this page is read from your browser's built-in screen and navigator objects using JavaScript that runs locally in your tab. Nothing about your display, viewport, or user agent is uploaded, logged, or stored. Closing the tab clears everything.
+Why does the checker show a smaller resolution than my monitor's native spec?
Most operating systems report logical resolution, which is affected by your display-scaling setting. If you run a 4K monitor at 150 percent scaling, the browser sees roughly 2560 by 1440 logical pixels even though the panel has 3840 by 2160 physical pixels. Check the Pixel Ratio and Physical Pixels values to see the native count behind the scaling.
+What's the difference between viewport and screen?
Screen size is the total monitor pixel area; viewport is what the browser tab occupies, after subtracting browser chrome (tabs, address bar, status bar). Viewport is what your CSS media queries respond to.
+What is device pixel ratio (DPR)?
DPR is the ratio of physical pixels to CSS pixels. A non-retina screen has DPR 1; macOS Retina is usually 2 (each CSS pixel = 2×2 physical pixels); some Android phones report 2.625 or 3. For sharp images on retina screens, serve images at DPR× the displayed size.
+Is my screen data sent anywhere?
No. The screen and viewport values come from browser APIs and are displayed locally. Nothing is uploaded or logged. Note: third-party fingerprinting scripts can read these same APIs — this tool just shows you the same data that any web page can already access.
Related Tools on Tooldit
Curious what else your browser reveals? Find your public address with the IP Lookup tool, or measure your connection with the Internet Speed Test. Like this checker, both run right in your browser.