Aspect Ratio Calculator
Calculate an image or video's simplified aspect ratio, and scale dimensions up or down while keeping that ratio — instantly inside your browser.
What is an aspect ratio?
An aspect ratio describes the proportional relationship between an image or video's width and height, written as two numbers like 16:9 or 4:3. Any two dimensions that share the same ratio look identically proportioned, just at different sizes — which is why resizing "while keeping aspect ratio" is such a common requirement in design and video work.
GuideHow to use it
How the calculation works
The simplified ratio is found using the greatest common divisor of the width and height, reducing them to the smallest whole numbers with the same proportion. When you type a new width or height, the other dimension is calculated by multiplying or dividing by that same original ratio, so the new size stays proportional to the original.
Why it helpsFeatures & benefits
Why this runs entirely in your browser
The calculation runs in JavaScript locally in the tab, which means it keeps working offline once the page has loaded and nothing entered here is ever sent to a server.
Common uses
Resizing an image or video without distorting it, figuring out what resolution to export a design at for a given ratio, or checking what aspect ratio a set of dimensions actually simplifies to.
Frequently asked questions
A few things people usually want to know before trusting the numbers.
It means the width is 16 units for every 9 units of height — the standard widescreen ratio used by most modern TVs, monitors, and video platforms.
Using the greatest common divisor of the width and height — dividing both by that number reduces them to the smallest whole numbers with the same proportion.
Yes — entering a smaller new width or height scales the other dimension down proportionally, just as entering a larger one scales it up.
Some real-world dimensions, like photos from a camera, don't land exactly on a standard ratio — the simplified ratio will still be mathematically accurate, just not a round number.
No. All calculation happens locally in your browser. Nothing entered here is sent to a server, stored, or shared.