Aspect Ratio Calculator Online
Calculate aspect ratios and scale dimensions for images and video
About this tool
Aspect Ratio Calculator Online is a free browser-based tool for working with image and video dimensions. Enter a width and height to instantly get the simplified aspect ratio, decimal ratio, and a full table of scaled sizes. Or enter a ratio and one known dimension to calculate the other — perfect for resizing images while keeping them proportional.
The tool includes presets for all major AI image generation formats (Midjourney, DALL-E, Stable Diffusion), social media platforms (Instagram, Twitter, YouTube, LinkedIn, OG image), video resolutions (720p, 1080p, 4K, cinema), and devices (iPhone, iPad). Click any preset to load its dimensions instantly.
All calculations run in your browser — no server, no upload, no signup.
Common use cases
- Find the correct aspect ratio for Midjourney --ar flag before generating images.
- Calculate scaled dimensions when resizing images for different screen sizes.
- Get the exact height for a given width while maintaining a 16:9 ratio.
- Check what aspect ratio a photo has before uploading to social media.
- Find dimensions for Instagram posts, stories, YouTube thumbnails, and OG images.
- Scale video frames up or down while maintaining the original ratio.
- Calculate canvas dimensions for AI image generators like DALL-E and Stable Diffusion.
- Generate a full set of responsive image sizes from a single source dimension.
- Verify that cropped images maintain the intended aspect ratio.
Frequently Asked Questions
What is an aspect ratio?
An aspect ratio is the proportional relationship between an image's width and height, expressed as two numbers separated by a colon — like 16:9 or 4:3. The same ratio can describe images of any size: 1920×1080, 1280×720, and 640×360 are all 16:9.
How do I use the Midjourney --ar flag?
The --ar flag accepts a ratio like --ar 16:9 or --ar 2:3. Use the Dimensions tab to enter your target dimensions and read the simplified ratio, or pick from the AI presets. Then add that ratio string to your Midjourney prompt.
How do I calculate height from a ratio and width?
Switch to the Ratio tab, enter your ratio (e.g. 16 and 9), select Width as your known dimension, enter the width value, and the tool instantly shows the correct height.
What is a 1.91:1 ratio?
1.91:1 is the Open Graph (OG) image ratio used by Facebook, LinkedIn, and Twitter for link preview cards. The standard size is 1200×630 pixels.
What does the decimal ratio mean?
The decimal ratio is the width divided by the height (e.g. 16/9 = 1.7778). It is useful for CSS aspect-ratio properties and for comparing different ratios numerically.
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