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Aspect Ratio — Free Online Tool
Aspect ratio describes the proportional relationship between an image or screen's width and height, and getting it right keeps videos from being stretched and photos from being cropped badly. This aspect ratio calculator takes a width and a height in pixels and reduces them to the simplest whole-number ratio using the greatest common divisor. Enter 1920 by 1080 and you get 16:9, the standard for HD video and most monitors; enter 1080 by 1350 and you get 4:5, the portrait format used on Instagram feeds; enter 1024 by 768 and you see 4:3. YouTubers can use it to check thumbnail and video dimensions, designers can confirm banner proportions, photographers can compare print sizes and developers can set responsive image containers. It is also handy when a website or ad platform asks for a specific ratio, because you can test your current size before resizing. If the ratio comes out unusual, such as 683:384, your dimensions are not an exact standard ratio and it is worth rounding to the nearest common size. To resize while keeping the same ratio, multiply or divide both sides by the same number. The tool works instantly in your browser with any whole-number dimensions and stores nothing.
Use our Aspect Ratio on AllConvertor — no registration, no download, works on iPhone, Android, Windows, and Mac. All processing runs in your browser when possible for maximum privacy and speed.
How to use Aspect Ratio
- Enter the width in pixels.
- Enter the height in pixels.
- Read the simplified ratio shown below the inputs.
- Resize both sides by the same factor to keep the ratio.
Key benefits
- ✓ 100% free — no paywall or trial limits
- ✓ No account or email required
- ✓ Mobile-friendly responsive design
- ✓ Instant results in your browser
- ✓ Secure — data stays on your device
- ✓ Trusted by thousands of users daily
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Frequently Asked Questions
How do I calculate aspect ratio?
Divide both width and height by their greatest common divisor. For 1920 × 1080 the divisor is 120, giving 16:9.
What is the aspect ratio of 1920×1080?
1920×1080 is 16:9, the common ratio for Full HD video, TVs, laptops and YouTube.
How do I resize an image without changing its aspect ratio?
Multiply or divide both the width and height by the same factor. For a 16:9 image of 1920 px width, a width of 1280 gives a height of 1280 × 9 ÷ 16 = 720.
What aspect ratio is best for Instagram and YouTube?
YouTube videos use 16:9, Instagram portrait posts use 4:5, square posts use 1:1 and Stories or Reels use 9:16. Platform specifications change, so confirm in their help pages.
Why does my ratio look strange like 683:384?
That happens when the dimensions do not match a standard ratio exactly. Adjust one side slightly to reach a common ratio like 16:9.