Aspect Ratio Calculator – Find Ratios and Resize Dimensions
Enter a width and height to see the simplified aspect ratio, or type a new width or height to get the matching size that keeps the image or video in proportion.
The aspect ratio is width ÷ height reduced to the smallest whole numbers: 1920 × 1080 becomes 16:9. To keep that ratio at a new width, multiply the new width by height ÷ width: 1280 × 1080 ÷ 1920 = 720, so 1280 × 720.
How to use Aspect Ratio Calculator
- Enter the original width and height, or pick a preset.
- Read the simplified ratio, the decimal ratio and the orientation.
- Type a new width to get the matching height.
- Or type a new height to get the matching width.
- Use the new size in your editor, camera or website.
What is aspect ratio?
The aspect ratio is the relationship between width and height. It is written as two numbers with a colon: 16:9 means 16 units wide for every 9 units high, whatever the actual size. A 1920 × 1080 video and a 1280 × 720 video both have a 16:9 ratio.
How to calculate it
Divide width and height by their greatest common divisor. For 1920 × 1080 the greatest common divisor is 120, so the ratio is 16:9. For awkward sizes like 1366 × 768, the exact ratio is 683:384, which is very close to 16:9 — the calculator shows such near matches too.
New height = new width × original height ÷ original width
Common aspect ratios
| Ratio | Typical sizes | Used for |
|---|---|---|
| 16:9 | 1920 × 1080, 3840 × 2160 | Video, YouTube, TVs, monitors |
| 9:16 | 1080 × 1920 | Stories, Reels, TikTok, Shorts |
| 4:3 | 1024 × 768 | Older screens, iPad, presentations |
| 3:2 | 6000 × 4000 | DSLR photos, prints |
| 1:1 | 1080 × 1080 | Square social posts |
| 4:5 | 1080 × 1350 | Instagram portrait posts |
| 21:9 | 2560 × 1080 | Ultrawide monitors, cinema |
Why keeping the ratio matters
If you change width and height independently, the picture is stretched or squashed: faces look wide, circles become ovals. Keeping the ratio when resizing avoids distortion. If the target space has a different ratio, you either crop the image or add bars (letterboxing).
Practical uses
- Planning video exports for different platforms.
- Sizing images for a website layout or a social media post.
- Checking whether a monitor or TV matches your content.
- Calculating print sizes that fit a frame.
Once you know the target size, resize your pictures with the Image Resizer, which offers the same ratios as presets, and shrink them with the Image Compressor.
Tip: export at the largest size you need and let the platform scale down, rather than enlarging a small file later.
You may also find these free tools useful: WebP to JPG Converter, Image Resizer and Image Compressor.
Frequently asked questions
How do I calculate an aspect ratio?
Divide the width and height by their greatest common divisor. 1920 × 1080 divided by 120 gives 16:9.
What size is 16:9?
Common 16:9 sizes are 1280 × 720, 1920 × 1080, 2560 × 1440 and 3840 × 2160.
How do I keep the aspect ratio when resizing?
Multiply the new width by original height ÷ original width to get the new height, or type the new width into the calculator.
What aspect ratio is best for Instagram?
Use 1:1 (1080 × 1080) or 4:5 (1080 × 1350) for feed posts and 9:16 (1080 × 1920) for Stories and Reels.
Is 1366 × 768 really 16:9?
Almost. The exact ratio is 683:384, about 1.779:1, which is very close to 16:9 (1.778:1).
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