Is my TV really 4K?

You paid for 4K, but the picture is not the jaw-dropper you expected, and now you are wondering whether you were sold a story. Usually the panel is genuinely 4K and something else is letting it down. Here is how to check all of it: The screen, the source, and the cable in between.

What "4K" actually means

4K means the screen is roughly 4,000 pixels wide. On a television that works out to 3840 by 2160 pixels, four times as many as Full HD at 1920 by 1080. More pixels means finer detail, but only when there is detail in the picture to show in the first place. You will see it written as 4K, UHD or 2160p, and on a TV those all mean the same thing. True DCI 4K, 4096 by 2160, is a cinema standard you will not run into on a home set.

Check the panel is 4K

Three ways, quickest first:

Run a resolution test. Open the Screen Resolution Test in the TV's own browser and it reports what the screen is working at. One catch worth knowing: A browser measures in a scaled unit, so a 4K TV often reads 1920 by 1080 at a pixel ratio of 2. Multiply the two and you are back to 3840 by 2160. The test does that sum for you.
Look in the settings menu. Plenty of TVs list the panel resolution under Settings, Support or About.
Look up the model number. The last word on it. Find the model on the back of the set or in the menu, search it, and the spec sheet states the native resolution plainly. If it says 3840 by 2160, 2160p or UHD, the panel is real 4K.

The bigger catch: Your source might not be 4K

This is where most people are actually short-changed. A 4K panel only shows 4K when something feeds it 4K, and often nothing is. The usual culprits:

The streaming plan. Netflix, Disney+ and the rest lock 4K behind their priciest tier. On a cheaper plan you are watching 1080p on a 4K screen, paying for a panel you never feed.
The content itself. Most live TV, all broadcast channels, and older films were simply never made in 4K. A 1080p stream or an ordinary Blu-ray is not 4K however good the television is.
The connection. 4K streaming needs roughly 25 Mbps of steady bandwidth. Below that, the app quietly drops you to HD to keep from buffering. The TV Internet Speed Test shows what your set is really getting.

Is the picture even reaching the TV in 4K?

Even with a proper 4K source, the signal still has to arrive intact.

The HDMI cable and port. For 4K at 60 frames a second, or 4K with HDR, you need a High Speed (18 Gbps) HDMI cable and a port that supports it. On many TVs some ports are slower than others, and the manual says which is which. A tired old cable is a common, completely invisible bottleneck.
Check the incoming signal. Most remotes have an info or status button that shows the resolution currently arriving from your box or console. If it reads 1080p while you are watching something you know is 4K, the source device or the cable is the weak link, not the TV.

For the fuller picture, the TV Capability Test reports the resolution, HDR signalling and codecs your set actually reports to the browser.

"Fake 4K" and marketing tricks

Genuinely fake 4K is rarer than the internet makes out. A handful of budget panels use an RGBW sub-pixel layout that reaches 3840 by 2160 dots but with fewer full-color sub-pixels, so fine detail can look a little softer than a standard RGB panel. It is still sold, quite legally, as 4K. The far more common effect is honest but easy to misread: upscaling. A 4K TV takes your 1080p picture and intelligently fills in the extra pixels. It really does look sharper than the same content on an old 1080p set, but it is not true 4K detail, and no upscaling can invent what was never filmed.

Questions people ask

My 4K TV looks the same as my old 1080p one. Why?

Most often it is the source: You are watching HD or broadcast content, not 4K. After that it tends to be seating distance (from across a big room the eye cannot resolve 4K detail on a mid-size screen), an over-processed picture mode, or motion smoothing. Feed it real 4K, sit a sensible distance away, and switch to Cinema or Filmmaker mode.

Does a 4K TV make 1080p content look better?

Somewhat, yes. A good 4K TV upscales HD to fill its panel, and a strong processor makes that look cleaner than 1080p shown on an older set. It is a real improvement, not a transformation, and it will never match content actually made in 4K.

Do I need a special HDMI cable for 4K?

For 4K at 30 frames a second, most existing cables cope. For 4K at 60 frames, or 4K HDR, you want a High Speed (18 Gbps) cable; for 4K at 120 frames for gaming, an Ultra High Speed (48 Gbps) one. The cable is cheap, and a mismatched one silently caps your resolution.

Two tools settle most of this in under a minute: The Screen Resolution Test confirms the panel, and the TV Capability Test reports the resolution, HDR and codecs your TV actually supports.