Aspect Ratio Calculator
Simplify any width × height into its aspect ratio, and work out the missing side for a target size — 1920×1080 becomes 16:9, instantly.
An aspect ratio is just a width and a height reduced to their simplest relationship — 1920×1080 and 1280×720 look different on a spec sheet but are the same shape, 16:9. This calculator does that reduction for any pair of pixel dimensions: enter a width and a height and it divides both by their greatest common divisor, shows the simplified ratio, the decimal form, and what that shape is commonly used for. It is the quickest way to answer “will this image fit that slot without distortion?” — if the ratios match, it scales cleanly; if they do not, something has to crop or stretch.
1 · Simplify a resolution to its ratio
2 · Resize while keeping a ratio
Pick a preset or type your own ratio, then change either side — the other side follows.
3 · Common resolutions — tap a row to load it above
| Name | Resolution | Ratio | Typical use |
|---|---|---|---|
| 480p | 854 × 480 | 16:9 | Standard-definition video |
| 720p HD | 1280 × 720 | 16:9 | HD video, older laptops |
| 1080p Full HD | 1920 × 1080 | 16:9 | Full HD video and monitors |
| 1440p QHD | 2560 × 1440 | 16:9 | QHD monitors |
| 4K UHD | 3840 × 2160 | 16:9 | 4K TVs and video |
| 8K UHD | 7680 × 4320 | 16:9 | 8K TVs |
| Square post | 1080 × 1080 | 1:1 | Instagram / social square |
| Portrait post | 1080 × 1350 | 4:5 | Instagram portrait |
| Vertical video | 1080 × 1920 | 9:16 | Shorts, Reels, TikTok, Stories |
| Social landscape | 1600 × 900 | 16:9 | X / Twitter card image |
Working with a real image file instead of numbers? The Image Resizer and the Resize tool change the file itself — use this page to decide which dimensions to give them.
How to use
About this tool
The second half works the other way round. Lock a ratio — type it in, or tap a preset such as 16:9, 9:16 for vertical video, 4:3, 3:2, 1:1 or 21:9 — then enter the width you need and the matching height is calculated, or enter a height and get the width. That is the everyday design and video question: a 1200 px-wide hero slot at 16:9 needs a 675 px-tall image; a Shorts frame at 9:16 from a 1080 width needs 1920 in height.
This page does the ratio maths only — it never touches an image file. If you have an actual picture to resize or crop to new pixel dimensions, use the Image Resizer or the freehand Resize tool instead, and come back here when you need to know what dimensions to ask them for. Everything runs in your browser; the numbers you type are not uploaded or stored.
Frequently asked questions
How do I calculate an aspect ratio?
Divide the width and the height by their greatest common divisor. For 1920×1080 the divisor is 120, giving 16:9. This calculator does it instantly and also shows the decimal form (16 ÷ 9 ≈ 1.78).
What aspect ratio is 1920×1080?
16:9 — the standard widescreen shape used by Full HD video, most monitors and most TVs. 1280×720, 2560×1440 and 3840×2160 (4K UHD) are the same 16:9 shape at different resolutions.
How do I resize an image without changing its shape?
Keep the ratio fixed and change one side: new height = new width × (ratio height ÷ ratio width). For a 16:9 image at 1280 wide, the height is 1280 × 9 ÷ 16 = 720. The resize section above does this in both directions.
What ratio should I use for YouTube Shorts, Reels or TikTok?
9:16 vertical — for example 1080×1920. Regular landscape video is 16:9, Instagram feed posts are commonly 1:1 (1080×1080) or 4:5 portrait (1080×1350).
What is the difference between this and the image resizer?
This calculator only works with numbers — it tells you which dimensions keep a shape. The Image Resizer and Resize tools change actual image files. Use this page to decide the target size, then those pages to produce it.
Are my numbers uploaded or stored?
No. The calculation runs in JavaScript in your browser. Nothing is sent to a server or kept after you close the page.
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