4K UHD screen size: 3840 by 2160
3840 by 2160 is the UHD display standard. It is exactly 16:9 and comes to 8.29 megapixels, four times the pixel count of Full HD.
At a glance
- Dimensions
- 3840 × 2160 pixels
- Simplified aspect ratio
- 16:9
- Decimal ratio
- 1.78:1
- Megapixels
- 8.29 MP (8,294,400 pixels)
- CSS aspect-ratio
- aspect-ratio: 16 / 9;
- Preset category
- Device
- Where it is used
- UHD displays, high resolution masters and downscaling sources
In detail
The name is a marketing compromise. 4K originally described the cinema format at 4096 pixels wide, and the consumer standard at 3840 wide is not four thousand of anything. It was named 4K anyway because it doubles both dimensions of Full HD and the 4K label had already stuck, which is why the pedantically correct name is UHD.
The distinction still matters in a video pipeline. Cinema 4K at 4096 by 2160 is a wider frame, about 1.90:1 against this 1.78:1, so mixing the two in one timeline produces either bars or a crop on every clip that came from the other standard. If a file is 4096 wide, it is not this format.
As a still image size it is the top of the practical range for browser based processing. At 8.29 megapixels a single decoded frame occupies tens of megabytes of working memory before any operation runs, so a tool that handles a 1080p image instantly can take a noticeable pause here. That is arithmetic, not a defect.
The image resizer has a 4K UHD preset and caps at 8192 pixels per side, so this canvas sits comfortably inside its range with room for the cinema width too. Downscaling from here to QHD or Full HD keeps the ratio exactly, because all three are 16:9.
Examples
3840 / 2160 = 1.7778 // 16:9, UHD
4096 / 2160 = 1.8963 // roughly 1.90:1, cinema 4K
// same height, 256 pixels of width apart3840 * 2160 = 8,294,400 pixels
8,294,400 * 4 bytes = about 33 MB decoded
// four times a 1080p frame, before any processing bufferThings that catch people out
- 4K names two different widths. Check whether a file is 3840 or 4096 before assuming the shape.
- Upscaling a 1080p source to this size adds pixels and no detail, at four times the file cost.
- Browser based image processing at this resolution needs real memory. Expect a pause, and expect a low end phone to struggle.
Try it: Aspect Ratio Calculator
Enter a width and a height, or a ratio and one dimension, and it solves the missing one, simplifies the ratio, counts the megapixels and gives you a copyable CSS value.
Aspect Ratio Calculator
LOCAL · Browser-OnlyCalculate and convert aspect ratios for images, videos, and screens
1920 x 1080px · 16:9 · 1.7778:1
Common Aspect Ratios Reference
| Ratio | Decimal | Common Use |
|---|---|---|
| 16:9 | 1.778 | Widescreen TV, YouTube, monitors |
| 4:3 | 1.333 | Classic TV, iPad, presentations |
| 1:1 | 1.000 | Instagram square, profile pictures |
| 21:9 | 2.333 | Ultrawide monitors, cinema |
| 9:16 | 0.563 | Phone vertical, TikTok, Reels |
| 3:2 | 1.500 | 35mm photography, MacBook |
| 2:3 | 0.667 | Portrait photography, posters |
| 5:4 | 1.250 | Large format photography, older monitors |
| 32:9 | 3.556 | Super ultrawide monitors |
| 2.39:1 | 2.390 | Anamorphic cinema, widescreen films |
Related Image and canvas sizes
All image and canvas sizes →1440p QHD screen size: 2560 by 1440
The 2560 by 1440 quad HD resolution, why quad refers to 720p rather than 1080p, and how it sits between Full HD and 4K in pixel count.
YouTube 4K video size: 3840 by 2160
The 4K UHD frame at 3840 by 2160, why it is exactly four times the pixel count of 1080p, and what uploading above the watched resolution actually buys you.
16:9 aspect ratio
Where the 16:9 ratio came from, the pixel dimensions that hit it exactly, what it suits, and the places where a widescreen frame is the wrong shape.
Ultrawide screen size: 3440 by 1440
The 3440 by 1440 ultrawide panel, why its true ratio is 43:18 rather than the advertised 21:9, and how it relates to a QHD display.
A4 at 300 DPI: 2480 by 3508 pixels
How 210 by 297 millimetres becomes 2480 by 3508 pixels at 300 DPI, why the A series ratio is the square root of two, and what bleed adds.
US Letter at 300 DPI: 2550 by 3300 pixels
How 8.5 by 11 inches becomes exactly 2550 by 3300 pixels at 300 DPI, the 17:22 ratio it reduces to, and why it does not interchange with A4.
Tools for this
- Image Resizer Free online image resizer - resize images to exact dimensions, percentage, or common presets
- Image Compressor & Resizer Compress images online free without uploading - reduce image file size in your browser with no quality loss