How to use the Aspect Ratio Calculator
- 1. Enter width and heightIn pixels, centimetres or any unit, as long as both match.
- 2. Add a new width or heightOptional: type one new side to get the other.
- 3. Use itCopy the ratio for CSS aspect-ratio, or the new size for exports.
Worked example
1920 × 1080 reduces to 16:9: the greatest common divisor of 1920 and 1080 is 120, and 1920 ÷ 120 = 16, 1080 ÷ 120 = 9. As a decimal that is 1.7778:1, the standard HD and YouTube shape. Enter a new width of 1280 and the tool returns 1,280 × 720, because 1280 ÷ 1.7778 = 720.
If a size does not reduce neatly, such as 1200 × 630 for link previews, the tool also shows the closest common ratio, here 1.91:1, and suggests a rounded size when the exact answer has decimals.
Common ratios and where they are used
- 1:1 square posts and profile images.
- 4:5 Instagram portrait posts; they take more screen space than squares.
- 9:16 Stories, Reels, Shorts and WhatsApp status.
- 16:9 YouTube, presentations and most screens.
- 4:3 iPads and older screens; 3:2 many cameras.
In CSS, aspect-ratio: 16 / 9; keeps an element in shape at any width, which avoids layout shift while images and videos load. Phone photos are often 4:3 while screens are 16:9, which is why some photos show bars or get cropped. Work with decimals and odd sizes freely: ratios are calculated from the exact numbers before rounding. For design proportions, try the golden ratio calculator; for social images, the poster maker has these sizes built in.
Frequently asked questions
Is 1366 × 768 really 16:9?
Almost. It reduces to 683:384, which is 1.7786:1, very close to 16:9's 1.7778. The tool shows it as about 16:9.
Does the unit matter?
No, as long as width and height use the same unit. A ratio has no unit.
Is the Aspect Ratio Calculator free?
Yes, the Aspect Ratio Calculator is free. The first time you see your first result, you are asked for your name and WhatsApp number once. After that, this and every other Uncodemy tool opens straight away without the form.