4K aspect ratio: UHD vs DCI
"4K" is two different formats. Consumer 4K UHD is 3840 × 2160 and is exactly 16:9. Cinema DCI 4K is 4096 × 2160 and is not — it is 256:135, about 1.896:1.
The numbers
| Format | Ratio | Pixels | Megapixels |
|---|---|---|---|
| 4K UHD (UHD-1) | 16:9 (1.778:1) | 3840 × 2160 | 8.29 |
| DCI 4K (full container) | 256:135 (1.896:1) | 4096 × 2160 | 8.85 |
| DCI 4K flat | 1.85:1 | 3996 × 2160 | 8.63 |
| DCI 4K scope | ≈ 2.39:1 | 4096 × 1716 | 7.03 |
| DCI 2K (full container) | 256:135 | 2048 × 1080 | 2.21 |
| 1080p Full HD | 16:9 | 1920 × 1080 | 2.07 |
| 1440p QHD | 16:9 | 2560 × 1440 | 3.69 |
| 5K | 16:9 | 5120 × 2880 | 14.75 |
| 8K UHD (UHD-2) | 16:9 | 7680 × 4320 | 33.18 |
| Ultrawide "5K2K" | 64:27 (2.370:1) | 5120 × 2160 | 11.06 |
Calculator
The presets cover the three shapes you meet in 4K work: 16:9 UHD, the 256:135 DCI container, and 2.39:1 scope.
Nearest standard resolutions
Where the two 4Ks came from
Digital cinema standardised first. The Digital Cinema Initiatives specification defined a 4096 × 2160 container — "4K" because the horizontal count is roughly four thousand pixels. Consumer television, meanwhile, had to stay compatible with the existing 16:9 HD ecosystem defined by ITU-R BT.709, so it doubled 1920 × 1080 in each direction to get 3840 × 2160 — the resolution standardised for consumer Ultra HD by ITU-R BT.2020. That is exactly four times the pixel count of 1080p, and exactly the same shape, which is why every 1080p asset scales into UHD with no reframing at all.
The two are 256 pixels apart in width and share the same height, so DCI 4K is about 6.7% wider than UHD. That is enough to matter: a graphic mastered for the DCI container and shown on a UHD display either loses 128 px from each side or gets thin bars.
Flat and scope inside the DCI container
A cinema projector shows one of two shapes inside the 4096 × 2160 container:
- Flat, 1.85:1 — 3996 × 2160. Full height, 100 px trimmed from each side of the container.
- Scope, ≈2.39:1 — 4096 × 1716. Full width, with the height reduced. 4096 ÷ 1716 is 2.3869, which the industry rounds to 2.39:1.
Notice that scope is not "letterboxed 1.85" — it uses the full width of the container and gives up height. When a scope film is released for a 16:9 television, the bars you see are added at that point, not baked into the cinema master.
Practical conversions
1080p to 4K UHD
Both are 16:9, so this is pure scaling: multiply both dimensions by 2. 1920 × 1080 becomes 3840 × 2160. No crop, no bars, no reframing. Upscaled 1080p footage inside a 4K timeline will never look as sharp as native 4K, but the geometry is free.
DCI 4K to 4K UHD
Enter 4096 × 2160 with the lock off — the ratio reads 256:135. To deliver 16:9 at the same height you need 3840 px of width, so 256 px must go: either crop 128 px from each side, or scale the full width down to 3840 and accept 2025 px of height, leaving about 68 px of black at the top and bottom of a 2160 px frame.
Scope inside a 16:9 delivery
Click the 2.39:1 preset and type 3840 into the width field: the height comes out at 1607 px. Placed centrally in a 2160 px tall UHD frame, that leaves about 276 px of black above and below — the familiar cinematic bars. If you need even numbers for encoding, use 1606 or 1608 and adjust the bars by one pixel.
Frequently asked questions
Is 4K 16:9?
4K UHD (3840 × 2160) is exactly 16:9. DCI 4K (4096 × 2160) is 256:135, about 1.896:1 — slightly wider. Almost everything a consumer meets, from streaming to TVs to phone cameras, is the 16:9 version.
Why is 4K UHD 3840 pixels wide and not 4096?
Because it was defined as exactly double 1920 × 1080 in each dimension, which preserves 16:9 and makes every existing HD asset scale perfectly. Choosing 4096 would have changed the shape and broken that compatibility.
How many pixels is 4K compared with 1080p?
Four times as many. 3840 × 2160 is 8,294,400 pixels; 1920 × 1080 is 2,073,600. The linear resolution — the detail across any one line — is only doubled, which is why the visible improvement is smaller than the pixel count suggests.
What ratio is an ultrawide 4K monitor?
A 3840 × 1600 panel is 12:5 (2.4:1) and a 5120 × 2160 panel is 64:27 (2.370:1). Both are marketed as "21:9", which is not what either of them actually is — true 21:9 is 2.333:1. See the main calculator, which lists the real panel sizes with their percentage offsets whenever you enter 21:9.
Should I shoot 4K if I deliver 1080p?
Usually yes, for reframing headroom. A 3840 × 2160 source lets you punch in to a 1920 × 1080 crop at 100% native resolution, stabilise without softening, or pull a 1215 × 2160 vertical crop for social — none of which a 1080p source can do without upscaling.
What comes after 4K?
8K UHD, 7680 × 4320, which is again exactly double in each direction and therefore still 16:9 — four times the pixels of 4K and sixteen times 1080p. 5K (5120 × 2880) sits between them and is also 16:9; it exists mainly as a monitor resolution because it fits a 4K video timeline with interface panels around it.
Does a 4K TV show DCI 4K content correctly?
It shows it, but not pixel-for-pixel. A 4096 × 2160 file on a 3840 × 2160 panel is either scaled to fit — producing 3840 × 2025 with small bars — or cropped. Since most home content is mastered in UHD, this rarely comes up outside of professional workflows.
Use cases & limitations
- Delivery specs. Confirm whether a client asking for "4K" means 3840 or 4096 pixels wide — the answer changes your framing.
- Timeline setup. Work out the exact letterbox height when placing a scope frame in a 16:9 sequence.
- Reframing budgets. Check how much crop a 4K master allows before you fall below your delivery resolution.
- Monitor buying. Read a panel's real ratio from its advertised pixel dimensions instead of trusting the marketing label.
- Limitation: pixel dimensions say nothing about bit depth, colour space, chroma subsampling or frame rate, all of which matter as much as resolution for perceived quality.
- Limitation: cinema camera makers use their own "4K", "4.6K" and "6K" sensor modes with varying ratios. Where a camera's mode is not one of the standards above, read its ratio off the actual pixel dimensions with the calculator rather than assuming.