Aspect Ratio Calculator
Calculate the aspect ratio of any width and height, or resize to a new size with the same ratio. Free online aspect ratio calculator for 16:9, 4:3 and 9:16.
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How to use Aspect Ratio Calculator
- 1Enter the original width and height, or tap a common ratio like 16:9, 4:3 or 9:16
- 2Read the simplified ratio, the decimal ratio and the closest standard format
- 3Type a new width or height to get the matching other side, then copy the new size
Frequently asked questions
How do you calculate aspect ratio?▾
Divide the width and height by their greatest common divisor. 1920 × 1080 share a divisor of 120, giving 16:9. The decimal form is width ÷ height = 1.78.
How do I resize an image and keep the aspect ratio?▾
New height = new width × original height ÷ original width. Scaling 1920 × 1080 to a width of 1280 gives 1280 × 1080 ÷ 1920 = 720, so the new size is 1280 × 720.
What aspect ratio is 1366 × 768?▾
Exactly 683:384 (1.78:1). It is marketed as 16:9 because it's within 0.1% of 1.7778.
Which aspect ratio should I use for social media?▾
16:9 for YouTube and landscape video, 9:16 for Reels, TikTok, Shorts and Stories, 1:1 for square posts and 4:5 for Instagram portrait posts.
What is 21:9?▾
An ultrawide ratio used by monitors like 2560 × 1080 (exactly 64:27, ≈ 2.37:1) and 3440 × 1440 (43:18, ≈ 2.39:1), close to the cinema scope format.
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