This 4K test checks whether a 4K monitor, TV or projector really shows all 3840 × 2160 pixels it is sent, one for one, without scaling them. The patterns are drawn at single pixel size: alternating one pixel lines, a one pixel checkerboard, single dots, tiny text, colored text, line wedges and a zone plate. The page also reads the resolution your browser draws at, so you can see at a glance whether the computer is sending 4K. Run it as a 4K monitor test when a new screen arrives. The same patterns work on any screen, from 1080p laptops to 5K and 8K monitors.
How to run the 4K test
- Set the computer to the screen's native resolution. In Windows, open Settings, then System, then Display, and choose the resolution marked Recommended. On a Mac, choose the size in Displays settings that looks like half the panel's resolution, such as 1920 × 1080 on a 4K screen, because macOS resamples the other scaled sizes.
- Leave your usual scaling on Windows. On 4K screens, 150% or 200% scaling is normal, and the test draws straight to screen pixels whatever the scaling.
- Press Start full screen test. The Pixel check comes first. The line at the top shows how many pixels the browser is drawing: 3840 × 2160 on a 4K UHD screen.
- Look at each tile from about 30 cm, then from your normal distance.
- Step through Fine text, Color text, Line wedges and the Zone plate.
- On a TV, set the picture size to Just Scan, Fit to Screen or Full Pixel first, so the TV does not zoom the picture.
What the results mean
| Pattern | On a screen that shows every pixel | When the picture is scaled |
|---|---|---|
| Pixel check readout | 3840 × 2160 on a 4K UHD screen | A smaller number: the computer sends less than 4K |
| 1 px lines and checkerboard | Every line separate up close, flat grey from afar | Grey mush, waves, bands or colored edges |
| Single pixels | Tiny dots in an even grid | Missing, doubled or smeared dots |
| Fine text | The 8 px line readable up close | Blurry or broken letters |
| Color text | Colored letters as sharp as white ones | Smeared colored letters |
| Line wedges | Lines separate down to the 1 px gap mark | Lines merging early or wobbling |
| Zone plate | Smooth rings, extra patterns only at the far edges | Extra ring patterns near the center |
The lines look grey, wavy or banded
When one pixel lines turn into grey mush or waves, something between the browser and the panel is resizing the picture. In order of likelihood:
- The computer is not at native resolution. A 4K monitor sent 2560 × 1440 or 1920 × 1080 has to stretch it. Set the Recommended resolution.
- The monitor or TV is zooming. Overscan on TVs and zoom or aspect settings on monitors resize the picture. Use Just Scan, Fit to Screen, Full Pixel or 1:1.
- Browser zoom. Reset it with Ctrl and 0, or Cmd and 0 on a Mac, if lines look uneven.
- A 4K projector with pixel shifting. Many 4K projectors place 8.3 million pixel positions with a smaller chip that shifts the image. One pixel patterns look softer on them, which is normal.
Colored text smears but white text is sharp
This is chroma subsampling. To save bandwidth, a signal can carry color at half or a quarter of the resolution of brightness, written 4:2:2 or 4:2:0. Black and white lines look fine, but small colored text and thin colored lines smear. It happens most over HDMI at 4K and 60 Hz or more, especially with HDR.
- Set the graphics card's output to RGB or YCbCr 4:4:4. In the NVIDIA Control Panel this is the output color format under Change resolution. In AMD Software it is Pixel Format under Display.
- Use DisplayPort, or an HDMI 2.1 port with an Ultra High Speed cable.
- On a TV, put the input in PC mode or Game mode. LG and Samsung TVs switch to PC mode when you set the input's icon or name to PC.
Is my screen really 4K?
| Name | Pixels | Where you see it |
|---|---|---|
| 4K UHD | 3840 × 2160 | 4K TVs, monitors and laptops |
| DCI 4K | 4096 × 2160 | Cinema projection, some pro monitors |
| 5K | 5120 × 2880 | Large high density monitors |
| QHD or 1440p | 2560 × 1440 | Many gaming monitors |
| Full HD or 1080p | 1920 × 1080 | Most budget monitors and TVs |
To check what your system reports outside this test, the screen resolution test lists screen size, scaling and the browser window. How sharp 4K looks depends on size: a 27 inch 4K monitor has about 163 pixels per inch, a 32 inch one about 138 and a 27 inch 1440p monitor about 109. The ppi calculator works it out for any screen.
4K at high refresh rates needs the right port
4K at 60 Hz needs at least HDMI 2.0 or DisplayPort 1.2. 4K at 120 or 144 Hz needs HDMI 2.1 or DisplayPort 1.4 or newer, and a cable rated for it, or the computer falls back to a lower refresh rate, a lower resolution or reduced color. After changing anything, confirm the rate with the refresh rate test. If the screen goes blank instead, see hdmi no signal.
4K TVs and projectors
Run the patterns from a laptop at 3840 × 2160, or save them at 3840 × 2160 with Save image and open them from a USB stick in the TV's or projector's media player. Many TV web browsers draw at 1920 × 1080 even on a 4K TV, so the readout in the TV's own browser may say 1920 × 1080 when the panel is 4K. The tv test pattern page covers the rest of a TV's picture settings, and the projector test pattern 4k set adds focus and convergence. For HDR on the same screen, run the hdr test.
What a browser 4K test cannot do
The readout shows the pixels your browser draws, which matches the screen when the computer runs at native resolution, but the page cannot read the panel's own resolution. In Chrome, Edge and Firefox the patterns land exactly on screen pixels at any Windows scaling. Safari cannot report exact device pixels, so keep its page zoom at 100% or one pixel lines can come out slightly uneven. A 4K test video is a weaker check than these patterns, because video compression and the player's scaling soften one pixel detail before it reaches the screen.
4K test questions
How can I tell if my monitor is really showing 4K?
Open the Pixel check pattern. The line at the top should read 3840 × 2160 pixels drawn, and up close every one pixel line should be separate and sharp. A smaller number means the computer is sending a lower resolution, and grey mush means something is scaling the picture.
Why does 4K look blurry on my monitor?
The usual causes are a lower resolution set in the display settings, a monitor or TV zoom or overscan setting, sharpness turned down, or color sent at reduced resolution over HDMI. The patterns here show which one it is.
Can I download a 4K test image?
Yes. Choose 3840 × 2160 under Image size and press Save image on any pattern. The PNG file is lossless, so every pixel stays exactly as drawn, unlike a 4K test video, which is compressed.
What is the difference between 4K UHD and DCI 4K?
4K UHD is 3840 × 2160, the resolution of 4K TVs and monitors. DCI 4K is 4096 × 2160, used in cinema projection and some professional monitors. Both are called 4K.
Why do the one pixel lines look grey from across the room?
That is normal. From a distance your eyes cannot separate lines one pixel apart, so they blend into grey. The test is to look from close up, where each line should be distinct, and to see no waves or bands from any distance.