Aspect Ratio Calculator

Find the aspect ratio of any size and calculate the missing width or height when resizing.

How do I calculate an aspect ratio?

An aspect ratio is the proportional relationship between width and height, written as width:height. It is found by dividing both numbers by their greatest common divisor — 1920 × 1080 becomes 16:9.

How to use

Enter the original width and height.
Optionally enter a new width or height — the calculator returns the matching other side.
Copy the CSS aspect-ratio value to reserve space for images and videos.

Formula

New height = new width × original height ÷ original width. Example: resizing 1920 × 1080 to a width of 1280 gives a height of 720.

Setting aspect-ratio (or width and height attributes) on images prevents layout shift while the page loads, which improves Core Web Vitals (CLS).

Frequently asked questions

What aspect ratio is 1080 × 1920?

9:16 — the vertical format for stories, Reels, TikTok and YouTube Shorts.

What ratio is 1200 × 630?

About 1.91:1, the recommended size for Open Graph link previews.

Why use the CSS aspect-ratio property?

It reserves the correct space for media before it loads, avoiding layout shifts.