Aspect Ratio Calculator
Pick a preset like 16:9, 9:16 or CinemaScope — or type your own ratio — and enter one dimension to get the other. Below the calculator is a full pixel reference for every common ratio at 1080p and 4K, what each platform expects, and the arithmetic behind letterbox and pillarbox bars.
Calculate width and height
Enter positive width and height ratio values to calculate dimensions.
Encoders that use 4:2:0 colour, which is nearly all H.264 and H.265 delivery, expect even numbers on both axes. If a result lands on an odd value, move it one pixel rather than letting the encoder pick.
Aspect ratios in pixels
| Ratio | As a decimal | 1080p | 4K | Inside a 1920 × 1080 frame | Typical use |
|---|---|---|---|---|---|
| 9:16 | 0.56:1 | 1080 × 1920 | 2160 × 3840 | 656 px each side | Reels, Shorts, TikTok, Stories — full-screen vertical. |
| 4:5 | 0.80:1 | 1080 × 1350 | 2160 × 2700 | 528 px each side | Instagram and Facebook portrait feed posts. |
| 1:1 | 1.00:1 | 1080 × 1080 | 2160 × 2160 | 420 px each side | Square feed posts and many ad placements. |
| 5:4 | 1.25:1 | 1350 × 1080 | 2700 × 2160 | 285 px each side | Legacy computer displays and print-style crops. |
| 4:3 | 1.33:1 | 1440 × 1080 | 2880 × 2160 | 240 px each side | Standard definition archive, Super 16, retro looks. |
| 3:2 | 1.50:1 | 1620 × 1080 | 3240 × 2160 | 150 px each side | Stills photography and open-gate camera modes. |
| 16:9 | 1.78:1 | 1920 × 1080 | 3840 × 2160 | Fills the frame | HD and UHD broadcast, YouTube, nearly every camera. |
| 1.85:1 | 1.85:1 | 1920 × 1038 | 3840 × 2076 | 21 px top and bottom | Cinema 'flat' theatrical release. |
| 1.9:1 | 1.90:1 | 1920 × 1010 | 3840 × 2022 | 35 px top and bottom | IMAX digital and the full DCI container. |
| 2:1 | 2.00:1 | 1920 × 960 | 3840 × 1920 | 60 px top and bottom | Univisium — common on streaming originals. |
| 21:9 | 2.33:1 | 1920 × 822 | 3840 × 1646 | 129 px top and bottom | Ultrawide monitors and some game capture. |
| 2.39:1 | 2.39:1 | 1920 × 804 | 3840 × 1606 | 138 px top and bottom | Cinema 'scope' widescreen. |
Ratios up to 16:9 are sized to a 1080 (or 2160) pixel height, wider ones to a 1920 (or 3840) pixel width, and vertical ones to a 1080 (or 2160) pixel width — the conventions the delivery specs actually use. Every value is rounded to an even number of pixels.
What each platform expects
| Placement | Ratio | Upload size | Notes |
|---|---|---|---|
| YouTube (landscape) | 16:9 | 1920 × 1080 | Upload up to 3840 × 2160 for a 4K option on the player. |
| YouTube Shorts | 9:16 | 1080 × 1920 | Anything squarer than 9:16 gets pillarboxed in the Shorts feed. |
| Instagram feed | 4:5 | 1080 × 1350 | Tallest ratio the feed shows without cropping. |
| Instagram Reels and Stories | 9:16 | 1080 × 1920 | Keep text away from the top and bottom 250 px for the UI overlay. |
| Instagram square | 1:1 | 1080 × 1080 | The safe third option: it reads the same in the feed and the grid. |
| TikTok | 9:16 | 1080 × 1920 | Same safe-area caution: captions and buttons sit over the edges. |
| Facebook feed video | 4:5 or 1:1 | 1080 × 1350 | Square is the safer choice for mixed desktop and mobile viewing. |
| X / Twitter | 16:9 | 1280 × 720 | Portrait plays too, but the timeline crops the preview. |
| LinkedIn feed video | 1:1 or 16:9 | 1080 × 1080 | Square wins more feed height on mobile. |
| Cinema — flat | 1.85:1 | 1998 × 1080 | DCI 2K flat container. |
| Cinema — scope | 2.39:1 | 2048 × 858 | DCI 2K scope container. |
Letterbox and pillarbox maths
When the picture and the frame disagree in shape, one pair of edges gets bars. Fit the picture to the limiting axis, then split the leftover space in half:
bar = (frame height − picture height) ÷ 2 · picture height = frame width ÷ ratio
- 2.39:1 in a 1920 × 1080 frame: 1920 ÷ 2.39 = 804 pixels of picture, leaving 138 px of letterbox above and below.
- 9:16 in a 1920 × 1080 frame: the height is the limit, so the picture is 608 × 1080 and 656 px of pillarbox sits on each side — the reason vertical video looks so small on a widescreen player.
- 4:3 in a 1920 × 1080 frame: 1440 × 1080 of picture with 240 px bars left and right.
Bars burnt into the file are permanent, which is fine for a scope look but wasteful for social: uploading 9:16 content at its own size beats uploading a pillarboxed 16:9 file, because the platform is not asked to encode 1312 pixels of black.
Frequently asked questions
What is 16:9 in pixels?
16:9 describes a proportion, not a size, so it has many pixel dimensions: 1280 × 720, 1920 × 1080, 2560 × 1440 and 3840 × 2160 are all 16:9. Divide width by height and you get 1.78 every time.
How do I turn a 1920 × 1080 video into 9:16?
The vertical delivery size is 1080 × 1920. You can crop the sides, which keeps the picture full-screen but loses two thirds of the frame, or fit the whole 16:9 image inside the vertical frame at 1080 × 608 and fill the remaining 656 pixels above and below with blur, colour or graphics.
Which aspect ratio should I use for Instagram and TikTok?
Use 9:16 at 1080 × 1920 for Reels, Stories, TikTok and YouTube Shorts. For the Instagram feed, 4:5 at 1080 × 1350 is the tallest ratio that is not cropped, and it takes up more screen height than a square post.
Why do width and height have to be even numbers?
H.264 and H.265 store colour at half resolution horizontally and vertically, so encoders expect both dimensions to be divisible by two. Odd dimensions either fail outright or get silently padded, which is why the tables here round to even pixels.
What is the difference between aspect ratio and resolution?
Resolution is the pixel count — 1920 × 1080. Aspect ratio is the shape those pixels form — 16:9. Two clips can share a ratio at wildly different resolutions, and a clip can keep its resolution while changing shape if the pixels themselves are not square.
What does 2.39:1 mean and how do I frame for it?
It is the modern cinema widescreen shape: the picture is 2.39 times wider than it is tall. Inside a 1920 × 1080 frame it occupies 1920 × 804 pixels with a 138 pixel black bar above and below, so shoot with that crop in mind and keep essential action out of the bars.
The same maths, pre-run for the values people ask about most.