Display test: dead pixels, colour, and refresh rate
Check your monitor or laptop screen for dead and stuck pixels, review full-screen colour swatches for banding or tint, confirm your true resolution and pixel density, and measure your actual refresh rate right in the browser.
Display test
Read your screen's real specs, measure its refresh rate, and open full-screen colour panels to hunt for dead pixels or banding.
Measured refresh rate
not measured
Full-screen colour panels
Quick guide: how to use the Display Test
Takes under a minute- 1Click the fullscreen icon for an accurate edge-to-edge test.
- 2Use Next and Previous to step through the solid colours and gradients.
- 3Look for stuck pixels, dust, backlight bleed and banding.
- 4Press Esc or Exit to leave fullscreen.
Overview
Every screen, whether it's a brand-new 4K monitor or a five-year-old laptop panel, is built from millions of individual sub-pixels that each need a working transistor to turn on and off correctly. Manufacturing at that scale means a small number of panels ship with imperfections, and years of use can introduce new ones through heat, pressure, or age. This test gives you a fast, structured way to check for those problems without needing any special software.
The tool above walks through three separate checks. First, full-screen colour swatches let your eyes scan for pixels that don't match the rest of the screen. Second, a display information panel reads your screen's real resolution, available space, colour depth, and device pixel ratio directly from the browser. Third, a refresh rate measurement times how many frames your screen is actually drawing per second, which you can compare against what your monitor is supposed to support.
Run through all three sections in order. Dead and stuck pixels are easiest to spot in a darkened room with your screen brightness turned up, since ambient light and glare can hide a single misbehaving pixel among millions of correctly working ones.
How to read your results
Colour swatches
Cycle through each full-screen colour, starting with black and white, then red, green, and blue, and finally grey. On black, look for any point of light that doesn't turn off. On white, look for any dark spot. On the pure red, green, and blue screens, look for a pixel that stays a different colour than its surroundings, since a healthy screen should look like one perfectly uniform colour across its entire surface, with no visible dots, lines, or blotches.
Display information panel
The numbers here describe your screen at a hardware and operating system level. Screen width and height are your monitor's full resolution. Available width and height subtract space used by taskbars or docks. Viewport size is how much space this browser window currently has. Device pixel ratio (DPR) tells you how many physical pixels are drawn per logical pixel, commonly 1 for standard monitors and 2 or more for high-density laptop and phone screens.
Refresh rate measurement
When you run the refresh rate check, the browser counts how many animation frames it can render in a fixed window of time and converts that into frames per second. A 60Hz monitor should read close to 60, a 120Hz or 144Hz gaming monitor should read close to those numbers, and a result well below what you expect usually means either your OS refresh rate setting is lower than your monitor's maximum, or your browser tab is being throttled by background activity.
Troubleshooting
If something looks wrong during this test, work through these steps:
- Wipe the screen with a microfiber cloth first. Many "dead pixels" turn out to be dust or a fingerprint smudge.
- Increase your screen brightness for the colour swatch tests, since dim panels make faint stuck pixels harder to see.
- Check your OS display settings and confirm the refresh rate dropdown is set to your monitor's maximum rather than a default value.
- Close other demanding applications and browser tabs before running the refresh rate measurement to avoid throttling.
- If using an external monitor, confirm the cable supports the resolution and refresh rate you expect; some HDMI and DisplayPort cables cap out below advertised specs.
- Try gently massaging a suspected stuck pixel with a soft cloth while displaying a black screen, which occasionally resolves stuck sub-pixels.
- If a dead pixel persists and your monitor is still under warranty, check the manufacturer's dead pixel policy before it expires.
Understanding resolution and pixel density
Resolution alone doesn't tell you how sharp a screen looks; pixel density does. A 24 inch monitor and a 32 inch monitor can both run at 1920x1080, but the smaller screen packs those pixels more tightly, producing a visibly sharper image. Device pixel ratio is the browser's way of accounting for this on high-density displays, scaling interface elements up so text and icons remain a comfortable, readable size instead of shrinking to a fraction of their intended size.
If your viewport dimensions look smaller than your screen resolution, that's expected. Taskbars, docks, browser chrome (the address bar and tabs), and window borders all take up space that isn't available to the actual page content, and the "available" measurements on this page already account for the first of those.
Why refresh rate matters
Refresh rate is how many times per second your monitor redraws the image on screen. Higher refresh rates make motion look smoother, which is especially noticeable when scrolling web pages, moving the mouse cursor, and playing fast-paced games. A 60Hz display redraws 60 times a second, while gaming monitors at 120Hz, 144Hz, or 240Hz redraw far more often, cutting down on motion blur and input lag.
Refresh rate is separate from frame rate, which is how many new images your graphics card is producing. Even a powerful GPU rendering 200 frames per second will only display 60 of them on a 60Hz monitor, so matching your monitor's refresh rate to your GPU's actual output, or enabling variable refresh rate technology like G-Sync or FreeSync, gets you the smoothest result.
Frequently asked questions
How do I test my monitor for dead pixels?
Use the full-screen colour swatches on this page and cycle through solid red, green, blue, white, black, and grey. A dead pixel stays black on every colour, while a stuck pixel shows a fixed colour (often red, green, or blue) regardless of what the rest of the screen displays.
What's the difference between a dead pixel and a stuck pixel?
A dead pixel has no power reaching it and always appears black. A stuck pixel is receiving power but one or more of its sub-pixels is stuck on, so it shows a constant colour like a tiny red or green dot even against a black background. Stuck pixels can sometimes be fixed; dead pixels usually cannot.
Can a stuck pixel fix itself?
Sometimes, yes. Gently massaging the area with a soft cloth while the screen shows a black image, or running a pixel-flickering video for 10 to 20 minutes, can unstick a sub-pixel in some panels. Dead pixels, which have no electrical signal at all, don't respond to this technique.
How many dead pixels are acceptable on a new monitor?
This depends on the manufacturer's policy, but most consumer panels allow a small number (often up to 3 to 5) before qualifying for a warranty replacement. Check your monitor brand's dead pixel policy before you buy or before your return window closes.
How do I test my monitor's refresh rate?
Use the refresh rate measurement on this page, which times a series of animation frames using your browser's rendering loop and calculates frames per second. For the most accurate reading, make sure no other demanding programs are running in the background.
Why does my refresh rate reading look lower than advertised?
Background load, browser tab throttling, power-saving settings, or an incorrect refresh rate set in your operating system's display settings can all cause a lower reading. Double check your OS display settings to confirm the refresh rate is actually set to your monitor's maximum before testing.
How do I check my screen resolution and DPI?
This page reads your screen and viewport dimensions directly from the browser and displays them alongside your device pixel ratio (DPR), which tells you how many physical pixels are packed into each CSS pixel on your specific display.
What does 'device pixel ratio' mean?
Device pixel ratio (DPR) describes the scaling between your operating system's logical pixels and the physical pixels of your screen. A DPR of 2 means every logical pixel is drawn using a 2x2 grid of physical pixels, which is typical of high-density laptop and phone screens.
Can I test an external monitor the same way?
Yes. Open this page in a browser window dragged onto the external display, or set it as your primary monitor, and the test will read that screen's resolution, color depth, and refresh rate just as it would for a built-in display.
Why do colours look different testing this way versus a colorimeter?
A colorimeter measures actual light output with a physical sensor, while this browser test only sends colour values to the screen and lets your eyes judge the result. It's excellent for spotting dead pixels, banding, or major colour casts, but it isn't a substitute for professional colour calibration.
My screen flickers only during this test, is that a problem?
Flicker that appears specifically on solid colour fields, especially grey, can indicate PWM (pulse width modulation) backlight dimming, which is a normal brightness control method on many panels but can cause eye strain for sensitive users at low brightness settings.