About the Aspect Ratio Calculator
A proportion tool for designers, developers, and anyone who works with images, video, or screen layouts.
What it does
The Aspect Ratio Calculator solves two common proportion problems in one place. Give it an aspect ratio plus one dimension and it instantly computes the other — so you never stretch or squash an image when resizing. Switch to Simplify mode and enter any width and height to get back the simplest ratio (like 16:9 from 1920×1080).
A live preview box updates in real time to show the exact proportion you're working with. Everything runs in your browser — nothing is stored or sent anywhere.
Features
Solve missing dimension
Enter a ratio and one known side (width or height) — the other is computed instantly and shown in the field. Change either value and the calculation updates bidirectionally.
Simplify any resolution
Type in a width and height — the tool divides both by their GCD to find the simplest integer ratio, plus the decimal equivalent for reference.
Common ratio presets
One-click buttons for 16:9, 4:3, 21:9, 1:1, 3:2, and 9:16 — the formats used in HD video, photography, ultrawide displays, social media squares, and vertical mobile content.
Live proportion preview
A scaled rectangle updates in real time to show the shape of the current ratio, so you can judge proportions visually without doing any mental math.
Non-integer warning
When the computed dimension is a fractional pixel (e.g. 562.5 from 16:9 at 1000 wide), the tool flags it immediately so you can round consciously rather than end up with a blurry edge.
Custom ratio input
Type any W:H ratio beyond the presets — including unusual ratios like 2.35:1 for anamorphic cinema or 5:4 for older monitors.
How the math works
All calculations use basic proportional arithmetic:
Solving from width
height = width × ratioH / ratioW
Example: 1920 × 9 / 16 = 1080
Solving from height
width = height × ratioW / ratioH
Example: 1080 × 16 / 9 = 1920
Simplifying a ratio
Both dimensions are divided by their greatest common divisor (GCD via Euclidean algorithm). 1920 and 1080 share GCD 120 → 16:9.
Decimal ratio
Width ÷ Height gives the decimal equivalent (1920 ÷ 1080 ≈ 1.7778). Useful when comparing ratios or matching values across tools that expect a single number.
Who it's for
Video editors
Match export dimensions to a target resolution without changing the ratio of the original footage.
Graphic designers
Scale artboards, banners, and print assets proportionally to any size — and check that a client-supplied resolution matches a standard ratio.
Web developers
Set correct width/height attributes on images, embed correct iframe dimensions, and design responsive containers that maintain layout proportions.
Photographers
Crop images to a target ratio for print sizes (4×6, 5×7, 8×10) and confirm the crop won't distort the original composition.
Social media managers
Find exact pixel dimensions for platform-required ratios — 1:1 for Instagram, 16:9 for YouTube, 9:16 for Reels and Stories.
Game developers
Scale sprite sheets and UI elements to any target resolution while preserving the original art's proportions across different screen sizes.
Completely free
No account required, no rate limits, no premium tier. Open it and use it — the calculation is instant and your data stays entirely in your browser.