Multi Monitor Detector
Multi Monitor Detector checks how many displays your system reports and lists each screen's resolution, color depth, and primary status in its own card — a permission prompt unlocks this automatically in Chromium browsers, and everywhere else you can add your monitors by hand using the same fields below. Enter each display's width and height manually if automatic detection isn't available on your browser, and get a running combined resolution total across every monitor you add. Handy when you're troubleshooting a monitor that Windows or macOS won't arrange the way you expect. The color gamut checker gives you a clear, actionable result instantly, with no sign-up required.
Detected Displays
Checking for the Window Management API…
Add Monitors Manually
How Browsers Detect Connected Monitors
Chromium-based browsers (Chrome, Edge, Opera, Brave) support the Window Management API, which lets a webpage — with your explicit permission — query how many displays are physically connected to your system and read each one's resolution, color depth, and position. This is the mechanism behind the live detection panel above: when you click Allow, the browser asks the operating system directly, so the result reflects your actual hardware setup rather than a guess based on browser window size. Use the screen size estimator any time you need a fast, accurate figure without doing the arithmetic yourself.
Firefox and Safari don't implement this API as of this writing, which is exactly why this tool includes a manual entry fallback — you can add each monitor by hand (its resolution and orientation) and the tool totals up the combined desktop space the same way, just without the automatic detection step.
Why the Permission Prompt Matters
Reading how many screens you have and their resolutions is genuinely sensitive information from a privacy standpoint — it can help fingerprint your device among millions of others, since the combination of monitor count, resolutions, and arrangement is fairly distinctive. Browsers gate this behind an explicit permission prompt for exactly that reason, and unlike simpler permissions (camera, location), the Window Management API requires a real user gesture — you have to interact with the page — before the browser will even show the prompt. If you decline, or your browser doesn't support the API at all, the tool simply falls back to the manual entry form with zero loss of core functionality. Use the free pixel ratio checker to confirm everything looks correct before you rely on it elsewhere.
Extended vs. Duplicated Multi-Monitor Setups
When more than one display is connected, your operating system can treat them in two fundamentally different ways:
| Mode | What It Does |
|---|---|
| Extended Desktop | Each monitor shows different content — your desktop effectively becomes larger, spanning across displays |
| Duplicated / Mirrored | Every monitor shows an identical copy of the same screen — common for presentations, where a laptop screen and a projector show the same slide |
This detector reports what the browser sees as distinct screens available to it, which in practice means it reflects the extended-desktop view — a mirrored/duplicated secondary display typically won't show up as an additional independent screen the same way, since from the OS's perspective it's showing the same content, not adding usable desktop space.
Troubleshooting When a Monitor Isn't Detected
If you know you have multiple displays connected but this tool only reports one, check a few common culprits: confirm the second display is actually receiving a signal (not just powered on) by checking your OS's own display settings first; make sure your browser is fully up to date, since Window Management API support was added relatively recently; and double-check that you clicked Allow rather than Decline on the permission prompt — you can usually reset a declined permission from your browser's site settings and reload the page to try again.
Frequently Asked Questions
- Why does this need a special permission instead of just working automatically?
- Your monitor count, resolutions, and arrangement can be used to help fingerprint your device, so browsers require explicit permission (and a real user click) before exposing this information to any webpage, this one included.
- Does this work in Firefox or Safari?
- Not for the automatic detection — the Window Management API is currently Chromium-only (Chrome, Edge, Opera, Brave). In Firefox and Safari, use the manual entry fields to add each monitor's resolution by hand and get the same combined totals.
- Will this detect a TV connected via HDMI the same way as a monitor?
- Yes — the browser doesn't distinguish device type, only that another display is connected and reports its resolution. A TV used as an extended display shows up the same as any other monitor.
- Why does my laptop's built-in screen count as one of the monitors?
- Because it is one — the built-in panel is a display like any other from the operating system's perspective, so it's included in the total alongside any external monitors you've connected.
- I have two monitors but they're mirrored — why does the tool only show one?
- In mirrored/duplicate mode, both displays show identical content, so the browser generally reports that as a single usable screen rather than two independent ones — switch to extended display mode in your OS settings if you want each monitor detected separately.