Aspect Ratio Calculator
This aspect ratio calculator finds the ratio of any size (1920 x 1080 is 16:9) and scales sizes up or down without stretching, with presets for YouTube, Reels, Instagram, phone photos and A4.
Find the ratio of a size
16:9
Decimal ratio 1.7778 : 1
Resize an image to 1920 x 1080 →Scale to a new size
1280 x 720
Common ratios
Popular sizes
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How to use Aspect Ratio Calculator
Type a width and height to see its ratio, or pick a popular size.
To resize, set the ratio (or pick a common one) and type the new width or height.
Use "Resize an image" to apply the size to a photo.
When to use Aspect Ratio Calculator
- Video creators. 16:9 for YouTube, 9:16 for Reels and Shorts.
- Social media. Instagram square, portrait and story sizes.
- Web design. Keep images and video embeds in proportion.
- Printing. A4 and other ISO paper sizes use a 1:√2 ratio.
Limits and privacy
- Everything runs in your browser. Nothing you type is sent or stored.
Frequently asked questions
What is 16:9 in pixels?
Any size where the width divided by the height is 1.778. Common 16:9 sizes are 1280 x 720 (HD), 1920 x 1080 (Full HD), 2560 x 1440 (QHD) and 3840 x 2160 (4K). YouTube thumbnails and most videos use 16:9.
What size is an Instagram post?
Use 1080 x 1080 pixels (1:1) for a square post, 1080 x 1350 (4:5) for a portrait post, which takes up more of the feed, and 1080 x 1920 (9:16) for stories and Reels. Instagram downsizes larger uploads to 1080 pixels wide.
How do I calculate aspect ratio?
Divide the width and height by their greatest common divisor. For 1920 x 1080 the GCD is 120, giving 16:9. To scale, keep the ratio: new height = new width x height ÷ width. For a 16:9 image 1280 pixels wide, the height is 1280 x 9 ÷ 16 = 720.
Related tools
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