Aspect Ratio Calculator
Scale dimensions while keeping the same proportions, find a missing width or height, and reduce any size to a simplified aspect ratio like 16:9. Everything runs in your browser — your data is never sent anywhere and nothing is stored.
Enter your original ratio, then fill in one new dimension — the other is calculated to keep the ratio.
Enter a width and height to see the simplified aspect ratio.
How to use the aspect ratio calculator
- Use Scale & find missing to resize while keeping proportions: type the original width and height, then one new dimension, and the other is filled in for you.
- Use Ratio from dimensions to turn any width and height into a clean aspect ratio such as 16:9 or 4:3.
- Click a preset to load a common ratio instantly. All results update live as you type.
Common ratios: 16:9 widescreen video and monitors, 4:3 classic fullscreen, 21:9 ultrawide,
1:1 square, 3:2 standard photography and 9:16 vertical phone video.
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Frequently asked questions
What is an aspect ratio?
An aspect ratio describes the relationship between the width and height of an image, video or screen, written as two numbers such as 16:9 or 4:3. It tells you the proportion of the shape regardless of its actual pixel size — a 16:9 image keeps the same proportions whether it is 1280×720 or 1920×1080.
How do I find a missing width or height?
Enter the original width and height (the ratio you want to keep) in the first row, then fill in one of the new dimensions in the second row. The calculator solves for the remaining value so the new size keeps the exact same proportions — for example 1920×1080 scaled to a width of 1280 gives a height of 720.
How is the simplified ratio calculated?
The width and height are divided by their greatest common divisor (GCD). For 1920 and 1080 the GCD is 120, so the ratio reduces to 16:9. This is the smallest whole-number form of the ratio.
What do common ratios like 16:9 and 4:3 mean?
16:9 is the standard widescreen ratio for modern TVs, monitors and online video. 4:3 is the older "fullscreen" format. 21:9 is ultrawide, 1:1 is a perfect square (common on social media), 3:2 is a classic photo format and 9:16 is vertical video for phones.
Is my data sent anywhere?
No. Every calculation runs entirely in your browser using plain JavaScript — nothing is uploaded to a server and nothing is stored.
Can I use decimals?
Yes. You can enter decimal values such as 1280.5 and the calculator will scale them proportionally. The simplified whole-number ratio is most meaningful for whole-pixel dimensions, but the decimal ratio is always shown too.