📐 Aspect Ratio Calculator

The Aspect Ratio Calculator computes the missing dimension when you know one side and the ratio (or one side and the other side, and you want the ratio). It's the small piece of arithmetic every designer, video editor, and photographer does dozens of times a week: what height should this hero image be at 1600 wide to stay 16:9? What width does a 1080-pixel-tall Instagram story need? Given a 3840 × 2160 file, what's the reduced ratio (16:9)?

How to Use This Tool

Either enter both dimensions to compute the ratio in lowest terms, or enter one dimension plus a target ratio (16:9, 4:3, 1:1, 21:9, or a custom pair) to compute the other dimension. The tool reduces ratios using GCD, so 1920×1080 correctly returns 16:9 rather than 240:135.

SEO Best Practices

Match your export sizes to the platform: YouTube expects 16:9, Instagram feed accepts 1:1, 4:5, and 1.91:1, Instagram Stories/Reels are 9:16, X post images ideally around 16:9 or 4:5. When resizing responsive images, keep the aspect ratio locked and let the browser pick the display size — never squash an image into a different ratio with CSS, since it distorts every face and object in it.

Example

A design brief specifies "16:9, 1600 pixels wide" — enter 1600 as width and 16:9 as target ratio, and the tool returns 900 as the required height. Or enter 3840×2160 to confirm it reduces to 16:9, useful when you've received a file and want to check it matches a spec.

Common Mistakes to Avoid

Don't confuse aspect ratio with resolution — 16:9 tells you nothing about how many pixels the image actually contains. Don't rely on ratio alone for OG images and social cards; each platform has a minimum pixel count too, and being too small triggers up-scaling that looks bad.