How to do it?
- 1.
Pick a ratio
Click a preset (e.g. 16:9) or type your own, e.g. 2.39 : 1.
- 2.
Enter one dimension
Type the width or height in pixels - the other is calculated instantly.
- 3.
Check a resolution
In the lower section enter e.g. 1366×768 to see its ratio and nearest standard.
Aspect ratio formula
height = width × (B ÷ A) and width = height × (A ÷ B). Example: 1920 px at 16:9 → 1920 × 9 ÷ 16 = 1080 px. To simplify a resolution, divide both sides by their greatest common divisor: 1920×1080 ÷ 120 = 16:9.
Vertical example: a Reel at 9:16 with a height of 1920 px needs 1920 × 9 ÷ 16 = 1080 px of width. Ultrawide example: 3440 px at 43:18 gives 3440 × 18 ÷ 43 = 1440 px.
Common aspect ratios and where they are used
| Ratio | Decimal | Typical resolutions | Used for |
|---|---|---|---|
| 16:9 | 1.778 | 1280×720, 1920×1080, 3840×2160 | YouTube, TVs, most monitors |
| 9:16 | 0.5625 | 1080×1920 | TikTok, Reels, Shorts, Stories |
| 4:3 | 1.333 | 1024×768, 1440×1080 | Old TV, slides, iPad, phone photos |
| 3:2 | 1.5 | 6000×4000 | DSLR and mirrorless photos |
| 21:9 | 2.33-2.39 | 2560×1080, 3440×1440 | Ultrawide monitors, cinema |
| 1:1 | 1 | 1080×1080 | Square social posts |
| 4:5 | 0.8 | 1080×1350 | Portrait Instagram and Facebook posts |
| 16:10 | 1.6 | 1920×1200, 2560×1600 | Laptops, office monitors |
“21:9” is a marketing label: 2560×1080 is exactly 64:27 (2.37:1) and 3440×1440 is 43:18 (2.39:1). The calculator shows both the exact simplified ratio and the nearest common one.
Why video dimensions should be even numbers
H.264 and H.265 usually store colour with 4:2:0 chroma subsampling, where colour is shared by 2×2 pixel blocks. Width and height therefore have to be even. If your calculation gives 562.2 px, use 562 - an odd value like 563 makes many encoders fail or crop the frame silently. The resolution table rounds heights to even numbers and marks inexact results with an asterisk.
Mistakes to avoid
- Stretching instead of cropping - forcing 4:3 footage into 16:9 without cropping makes faces 33% wider. Crop or add black bars instead.
- Swapping the numbers - width always comes first. 1080×1920 is vertical (9:16), 1920×1080 is horizontal (16:9).
- Confusing ratio with resolution - 1280×720 and 3840×2160 share the same 16:9 ratio but have nine times fewer or more pixels.
Once you know the target size, you can change the format of a clip with the video converter.
Frequently asked questions
What height is 1920 wide at 16:9?
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What ratio is 1366×768?
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What format do TikTok and Reels use?
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What is the difference between 16:9 and 16:10?
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Can I enter a decimal ratio like 2.39:1?
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What size is a 4:5 Instagram post?
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