Dead Pixel & Screen Test
Fill the screen with solid colours to spot dead or stuck pixels, and see your screen’s specs.
How to use Dead Pixel & Screen Test
- Clean the screen, then press Start the full-screen test.
- Each colour fills the whole screen. Look closely from about 30 cm. Click, or press → or Space, for the next colour; ← goes back; Esc exits.
- A dot that stays black on white is a dead pixel; a dot that stays bright or coloured on black is a stuck pixel. The side panel shows your screen’s resolution, scaling, refresh rate and colour support.
Dead, stuck and what the numbers mean
Each pixel of an LCD or OLED screen is made of red, green and blue sub-pixels. A dead pixel stays dark whatever is shown and is easiest to see on white. A stuck pixel stays lit in one colour and shows on black or on the other primary colours. Solid red, green and blue screens reveal a single faulty sub-pixel. The grey screen helps you judge uniformity, banding and backlight bleed (brighter patches near the edges, best checked in a dark room on the black screen).
The screen resolution shown is the physical pixel count: the size your system reports in CSS pixels multiplied by the scaling factor (device pixel ratio). A 4K laptop panel at 150% scaling reports 2560 × 1440 “CSS” pixels but has 3840 × 2160 real ones. The refresh rate is measured by counting how often the browser draws in one second; it shows the rate the screen is running at now, which may be lower than its maximum if power saving is on.
Colour gamut and HDR come from the browser’s media queries: “Display P3” means a wide-gamut screen (most recent Macs and phones), and HDR means the screen and system are in high-dynamic-range mode.
Example
A laptop reports 1536 × 864 CSS pixels at 125% scaling: the panel is 1920 × 1080 (Full HD), 16:9, sRGB, measured at about 60 Hz. A gaming monitor at 2560 × 1440 shows about 144 Hz once 144 Hz is selected in the display settings.
Frequently asked questions
How do I check for dead pixels?
Press Start and look at each solid colour closely. A spot that stays black on the white screen is a dead pixel; a spot that stays coloured or bright on black is stuck.
Can a stuck pixel be fixed?
Sometimes. Stuck pixels occasionally recover after hours of rapidly changing colours or gentle pressure with a soft cloth while the screen is off (at your own risk). Dead pixels, which stay dark, usually cannot be fixed; check the manufacturer’s pixel policy and warranty.
What is my screen resolution?
The side panel shows it: the physical resolution, the scaled size your system uses and the scaling percentage. The browser window size is shown separately.
Why does the refresh rate show 60 Hz on my 144 Hz monitor?
The measurement shows the rate the screen is running at now. Select the higher rate in your display settings (Windows: Settings → Display → Advanced display), check the cable (DisplayPort or HDMI 2.0+), then reload the page.
Does this work on phones and TVs?
Yes. On phones the colours fill the browser window; on iPhones without full-screen support, hide the toolbars by scrolling or turning the phone sideways.
Limitations
- Refresh rate is measured from the browser’s drawing rate and can read low if the computer is busy or in battery saver.
- Phones may keep a status bar visible where the browser does not allow full screen.
- Physical resolution assumes the system reports its scaling accurately (true on Windows, macOS, Android and iOS).
Guides for this tool
- Dead Pixel vs Stuck Pixel: Check a Screen in 2 MinutesHow to spot dead and stuck pixels, backlight bleed and a wrong refresh rate on a new or used monitor, laptop or phone, and what you can do about each.
Last reviewed November 9, 2026. How we build and test tools.