Aspect Ratio Calculator
Instantly simplify any width/height pair to its exact aspect ratio, or scale a known ratio to any new dimension. Runs entirely in your browser.
1920 × 1080 simplifies to 16:9
What is an aspect ratio calculator?
An aspect ratio calculator helps you work with proportional dimensions quickly and accurately. Whether you are cropping a photograph, configuring a video export, setting CSS on an embedded player, or specifying artboard sizes in a design tool, knowing the exact ratio — and being able to scale it to any size — saves time and prevents distortion.
Two modes in one tool
- Simplify ratio — enter any width and height (e.g. 1920 × 1080) and the tool reduces the pair to its lowest terms using the greatest common divisor, giving you the canonical ratio (16:9 in this example).
- Scale to dimension — enter a target ratio and one known dimension (width or height) to calculate the missing value. Perfect for resizing assets while preserving proportions.
Common aspect ratios
The most widespread ratios today are 16:9 (HD and 4K video, most monitors), 4:3 (legacy screens and many tablet cameras), 1:1 (square social media posts), and 9:16 (vertical short-form video). Cinema uses ratios like 2.35:1 (anamorphic widescreen) and 1.85:1 (flat widescreen).
Runs entirely in your browser
All calculations happen client-side using pure arithmetic — no images are uploaded, no data leaves your device. The tool works offline once the page is loaded.
Frequently Asked Questions
What is an aspect ratio?↓
An aspect ratio expresses the proportional relationship between a rectangle's width and height, written as W:H. For example, a 1920×1080 screen has an aspect ratio of 16:9 because dividing both numbers by their greatest common divisor (120) gives 16 and 9. Aspect ratios are used everywhere from video production and photography to responsive web design and screen specifications.
How do I find the missing dimension for a given ratio?↓
Switch to the "Scale to dimension" tab, enter the target ratio (e.g. 16 and 9), then type either a width or a height. The calculator instantly computes the other value by multiplying or dividing by the ratio. This is useful when resizing images or setting iframe dimensions without distorting the original proportions.
Why does my ratio not simplify to what I expected?↓
The simplification uses integer GCD reduction after rounding your inputs to the nearest whole pixel. Non-standard resolutions — such as 2560×1080 (ultrawide) — reduce to ratios like 64:27 rather than the commonly advertised 21:9, because 21:9 is a marketing approximation. The calculator shows the mathematically exact simplified form.