Aspect Ratio Calculator
Aspect ratio
:
16:9
1.778 : 1
Resize keeping this ratio
Type a new width or height and the ratio stays fixed — the other value fills in to match.
:
Find the aspect ratio of any width and height, then resize while keeping the ratio — no stretching. One-tap presets for 16:9, 4:3, 21:9 and more. Free, instant, nothing to install.
How to Use the Aspect Ratio Calculator
1
Enter width and height
Type any width and height, or tap a preset. The tool shows the simplified ratio (like 16:9) and the decimal ratio.
2
Resize to fit
Enter the new width you need and the matching height appears automatically — or enter a height to get the width — so nothing is stretched.
3
Use it anywhere
Scale photos, video frames, thumbnails, ad units or design elements to fit a space while keeping the proportions exact.
Frequently Asked Questions
How do I calculate an aspect ratio?
An aspect ratio is the width divided by the height, written as two numbers separated by a colon such as 16:9. To reduce any width and height to a clean ratio, divide both by their greatest common divisor — for example 1920 by 1080 both divide by 120, giving 16:9. This calculator does that automatically and also shows the decimal ratio.
How do I resize while keeping the aspect ratio?
Set the original width and height to define the ratio, then type the new width you want and the calculator fills in the matching height automatically — or type a new height to get the width. Because both new dimensions come from the same ratio, the image or video is never stretched or squashed.
What are common aspect ratios?
The most common ratios are 16:9 for modern TVs, monitors, YouTube and most video; 4:3 for older screens and many photos; 21:9 for ultrawide monitors and cinematic video. Square 1:1 suits social posts, 3:2 suits many cameras and prints, and 9:16 suits vertical phone video and stories. The calculator includes one-tap presets for all of these so you can jump straight to a ratio and resize from it.
Is anything uploaded or saved?
No — this aspect ratio calculator runs entirely in your browser with plain arithmetic, so nothing is uploaded, stored or shared. You are only entering numbers. There is no sign-up, and it works offline once loaded, on phone, tablet or desktop.
Related tools
More free front-end helpers: the CSS Grid Generator, the Flexbox Generator and the Color Contrast Checker.