How is the aspect ratio simplified?

The calculator determines the Greatest Common Divisor (GCD) between width and height to produce the simplest whole-number ratio (e.g. 1920x1080 simplifies to 16:9).

How do I use the proportional resize tool?

Enter your original width and height, then type your new target width to automatically calculate the exact proportional target height.

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Converters

Aspect Ratio Calculator

Calculate 16:9, 4:3, 21:9 image and video aspect ratios with proportional resizing.

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How to Use Aspect Ratio Calculator

Enter original width and height in pixels (or pick a standard preset like 16:9 or 4:3).
Inspect the automatically simplified ratio (W:H).
Enter a new target width to calculate the proportional height.
Copy the modern CSS aspect-ratio snippet.

Frequently Asked Questions

How is the aspect ratio simplified?: The calculator determines the Greatest Common Divisor (GCD) between width and height to produce the simplest whole-number ratio (e.g. 1920x1080 simplifies to 16:9).
How do I use the proportional resize tool?: Enter your original width and height, then type your new target width to automatically calculate the exact proportional target height.

Sources & References

Primary references: MDN: CSS gradients; WHATWG HTML Living Standard.

Review policy: references and behavior notes are checked whenever the tool implementation changes.