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Detect aspect ratios, calculate dimensions for 16:9, 4:3, 21:9 and more.
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Among ToolsMonk's converters, Aspect Ratio Calculator covers a single everyday need: detect aspect ratios, calculate dimensions for 16:9, 4:3, 21:9 and more. Open the page and start working, with no download or sign-up standing between you and the result.
Typical jobs it handles include resizing an image or video without distorting it, finding the height for a given width at 16:9 (or any ratio), and working out the ratio of existing dimensions. The same page works on desktop, tablet, and mobile, so it is equally quick for a single urgent task and for work you repeat every week.
Everything about Aspect Ratio Calculator is tuned for speed to first result, with privacy-friendly processing and the rest of ToolsMonk's tools nearby when the next task comes up.
| Price | Free, no signup, no paywall, no watermark |
|---|---|
| Works on | Any modern browser: desktop, tablet, and mobile |
| Processing | In your browser, files never leave your device |
| Account required | None |
| Category | Converters |
Enter the aspect ratio (or pick a preset)
Enter the width OR height you know
The tool calculates the matching other dimension
Use the values to resize without stretching
Calculates a missing width or height to keep a target aspect ratio
Works with common ratios (16:9, 4:3, 1:1, 21:9) or a custom ratio
Simplifies given dimensions to their ratio
Instant results as you type
Runs in your browser, nothing is uploaded
Free, with no signup and no cap on conversions
Resizing an image or video without distorting it
Finding the height for a given width at 16:9 (or any ratio)
Working out the ratio of existing dimensions
Planning layouts, thumbnails, and embeds to a fixed proportion
At its core, Aspect Ratio Calculator does one thing well, detect aspect ratios, calculate dimensions for 16:9, 4:3, 21:9 and more, with instant, accurate results. There is no software to install and no account to create; the tool is ready the moment the page loads.
As part of our Converters collection, this tool is designed with simplicity and power in mind. All processing runs locally in your browser, so your files and data never leave your device. The tool works seamlessly across all modern browsers on desktop, tablet, and mobile devices.
Aspect Ratio Calculator keeps your dimensions proportional. Give it a ratio and one dimension, and it computes the other so an image or video resizes without stretching; give it two dimensions, and it simplifies them to their ratio so you can identify the format.
The core idea is that aspect ratio is shape, independent of size. A 16:9 frame is always the same proportion whether it's 1920×1080 or 1280×720, so to scale without distortion you change one dimension and let the ratio dictate the other, exactly the calculation the tool automates.
Common ratios map to real uses: 16:9 for modern video, monitors, and YouTube; 4:3 for older displays and some slides; 1:1 for square social posts; 21:9 for ultrawide. Presets make these one click, while a custom ratio handles anything else.
The calculator works out dimensions but doesn't alter pixels, so to actually re-shape an image to a new ratio you'll crop or pad it, the Crop Image tool offers matching ratio presets. Everything runs in your browser with nothing uploaded.
Change one dimension and let the calculator set the other, that's how you resize without distortion
Use it to find a 16:9 height (width × 9 ÷ 16) for video thumbnails and embeds
To actually re-shape an image to a new ratio, pair it with Crop Image's ratio presets
Common questions about this tool, its workflow, and what to expect before you use it.
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Preview
Detect aspect ratios, calculate dimensions for 16:9, 4:3, 21:9 and more.
Use Aspect Ratio Calculator free →Live tool (iframe)
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