4K Resolution: UHD vs DCI 4K, Pixel Counts and PPI

By Aspect Ratio Calculator Pro Editorial Team · Updated Oct 30, 2026

"4K" is a nickname for a picture about 4,000 pixels wide, and it covers two different sizes. Your TV, monitor, game console and streaming apps use 3840 × 2160 (4K UHD). Movie theaters use 4096 × 2160 (DCI 4K). This guide gives the exact numbers for both, shows them to scale against 1080p, and works out pixel density and viewing distance for common screen sizes.

What is 4K resolution?

4K resolution means a frame roughly 4,000 pixels wide and 2,160 pixels tall. Two standards define it:

• 4K UHD, 3840 × 2160. The ITU's ultra-high-definition TV standard, Recommendation ITU-R BT.2020, lists two picture sizes: 3840 × 2160 and 7680 × 4320 (8K). Both are 16:9 with square (1:1) pixels and progressive scan. BT.2020 allows frame rates from 23.976 up to 120 Hz.
• DCI 4K, 4096 × 2160. The Digital Cinema System Specification from Digital Cinema Initiatives defines a 4K distribution as one whose image container is 4096 × 2160, and a 2K distribution as 2048 × 1080. Its decoder section lists 4K as "4096x2160 at 24 FPS".

Unless you work in cinema mastering or projection, "4K" on a product box or upload screen almost always means 3840 × 2160.

Is 4K the same as UHD?

Not exactly, but in consumer products the two labels mean the same thing. The Consumer Technology Association's Television Technology Consumer Definitions say a display may be called "4K Ultra High-Definition" if it has at least 8 million active pixels, with at least 3840 horizontally and at least 2160 vertically. The same definition also requires:

• a native resolution with a width-to-height ratio of 16:9 or wider
• one or more HDMI inputs that accept native 3840 × 2160 at 24p, 30p and 60p, with at least one supporting HDCP 2.2 or equivalent copy protection
• the ability to upscale HD video to the panel's full resolution
• a minimum bit depth of 8 bits

So "4K UHD" on a TV is a minimum spec. A screen with more pixels than 3840 × 2160 still qualifies, but one with fewer does not. DCI 4K is a cinema format, and you rarely see it on consumer TVs.

What does 2160p mean?

2160p names the picture height. The number is the count of pixel rows (2160) and the "p" means progressive scan, so every line is drawn in every frame. BT.2020 defines only progressive scan for UHD, so the standard has no interlaced 2160i format.

Both 4K variants are 2160 pixels tall. Only the width changes, so "2160p" alone doesn't tell you whether a file is 3840 or 4096 wide. For consumer video it means the 16:9 BT.2020 frame, 3840 × 2160; the CTA definition above also uses "2160p" for 4K UHD inputs.

How many pixels and megapixels is 4K?

Multiply width by height:

A few relationships worth remembering:

• 4K UHD is exactly 4× 1080p. Both dimensions double (1920 × 2 = 3840, 1080 × 2 = 2160), so the pixel count goes up four times. That is why 1080p content scales to a 4K panel cleanly: each source pixel becomes a 2 × 2 block.
• DCI 4K is exactly 4× DCI 2K. 2048 × 2 = 4096 and 1080 × 2 = 2160. The DCI spec requires projectors to do 2K-to-4K conversion at an exact 2:1 ratio in each axis.
• DCI 4K has 552,960 more pixels than 4K UHD, about 6.7% more, all of it in extra width.
• 4K UHD has 2.25× the pixels of 1440p, because each side is 1.5× longer (2560 × 1.5 = 3840).
• 8K is 4× 4K UHD, the same doubling again.

To check any of these ratios yourself, enter the width and height in the Aspect Ratio Calculator.

What aspect ratio is 4K?

• 3840 × 2160 is 16:9. Divide both sides by 240 and you get 16 × 9. It is the same shape as 1080p, 1440p and 720p, so 16:9 video fills a 4K TV with no black bars.
• 4096 × 2160 is 256:135, which is about 1.90:1. Divide both sides by their greatest common divisor, 16, and you get 256 × 135.

A film whose aspect ratio differs from 1.90:1 is placed inside the 4096 × 2160 container rather than filling it. The DCI spec points to SMPTE 428-1 for those image characteristics. If you need the exact active area of a specific DCP, check the delivery specification for that project.

4K vs 1440p vs 1080p

The non-integer step matters. 1080p fits a 4K panel as clean 2 × 2 pixel blocks, but 1440p needs 1.5× scaling, and the screen has to interpolate. For the details on each format, see the 1080p resolution guide and the 1440p resolution guide. "2K" is a separate confusion: the DCI meaning is 2048 × 1080, not 2560 × 1440. The 2K resolution guide explains why.

How many pixels per inch is a 4K monitor or TV?

Pixel density depends on screen size. For a 16:9 screen, PPI = √(width² + height²) ÷ diagonal in inches. For 3840 × 2160 the diagonal is √(3840² + 2160²) ≈ 4,405.8 pixels, so you divide that by the screen size:

Our calculation from the formula above; pixel pitch = 25.4 mm ÷ PPI.

Two things stand out. A 55-inch 4K TV and a 27-inch 1080p monitor have almost the same density (about 80 PPI), so a 4K TV looks sharp mainly because you sit farther away. A 27-inch 4K monitor packs 163 PPI, which makes text very small at 100% scaling. At 150% scaling, 3840 × 2160 gives the same layout space as 2560 × 1440 (3840 ÷ 1.5 = 2560), with sharper text. To convert between inches and pixels for a specific screen, use Inches to Pixels.

How far should you sit from a 4K TV?

Recommendation ITU-R BT.1845 defines the optimal viewing distance as the point where one pixel subtends an angle of 1 arc-minute, which is about the limit of normal visual acuity. Its Table 1 gives:

• 3840 × 2160: 1.6 picture heights (1.6 H), a 58° horizontal viewing angle
• 1920 × 1080: 3.2 picture heights (3.2 H), a 31° horizontal viewing angle

Converted to real 16:9 screen sizes (picture height = diagonal × 9 ÷ √337):

Our arithmetic using the BT.1845 picture-height multiples.

Read this the other way around. If you sit farther back than the 1080p figure, normal eyesight can't resolve individual 1080p pixels on that screen, so the extra detail of 4K is hard to see at that distance. Sit closer, or buy a bigger screen, and the gain becomes visible. These figures assume average acuity, so treat them as a guide rather than a rule.

Is my file 4K?

Check its pixel dimensions, not the file name or the export preset label. Drop an image or a full-size exported video frame into the Image Resolution Checker. It reads the width, height, megapixels and aspect ratio in your browser without uploading the file.

• 3840 × 2160 is 4K UHD.
• 4096 × 2160 is DCI 4K.
• Width 3840 or 4096 but height under 2160 (for example, a wide film crop) means a 4K-wide frame with a wider aspect ratio, not full 2160p.
• Anything at 1920 × 1080 or below is HD, even if the file was "upscaled" or labeled 4K.

To check the screen you are viewing this on rather than a file, use What Is My Screen Resolution. It reports the screen size and device pixel ratio, so you can tell whether a 4K panel is running at a scaled resolution.

Common 4K mistakes

• Treating "4K" as one number. Consumer TV and streaming 4K is 3840 × 2160 (BT.2020); cinema 4K is 4096 × 2160 (DCI). If a client asks for 4K, confirm which one.
• Assuming 4K means 4× the sharpness. It means 4× the pixels of 1080p but only 2× the linear resolution. Whether you can see the difference depends on screen size and distance (see the tables above).
• Scaling 1440p up to 4K and calling it 4K. Upscaling raises the pixel count but adds no new detail.
• Cropping a 16:9 4K frame to a different ratio without checking the result. A 2.39:1 crop of a 3840-wide frame keeps the width but loses height. Work out the new size with the Aspect Ratio Calculator before you export.

How this guide was made: an AI tool helped with research and the first draft, and we then checked each figure against the sources above. Found an error? Email editorial@aspectratiocalculatorpro.com. Editorial policy.

Related

• 1080p Resolution: 1920 × 1080 Pixels Explained1080p resolution is 1920 × 1080 pixels (16:9, 2,073,600 px). What the p means, 1080p vs 720p, 1440p and 4K, PPI by screen size, and other-ratio sizes.
• What Is 1440p Resolution? 2560 × 1440, QHD and WQHD1440p is 2560 × 1440 at 16:9, sold as QHD or WQHD. Exact pixel counts, PPI by screen size, ultrawide 1440p math and 125%/150% scaling tables.
• What Is 2K Resolution? Cinema 2K vs. 2K Monitors2K resolution officially means the DCI cinema container, 2048 × 1080. Monitors sold as 2K are usually 2560 × 1440. Exact pixel counts, ratios and diagrams.
• Aspect Ratio CalculatorWork out any width, height or ratio.