How to use the aspect ratio calculator
- 1Enter the original width and height, or pick a common ratio such as 16:9.
- 2Read the ratio in lowest terms and as a decimal.
- 3Type a new width or height. The other value is worked out to keep the same shape.
- 4Click a common size to use it, then copy the result.
What an aspect ratio is
An aspect ratio describes the shape of a rectangle: width compared with height. A 1920 × 1080 video and a 1280 × 720 video are different sizes but the same shape, 16:9.
To find the ratio, the calculator divides both numbers by their greatest common divisor. 1920 and 1080 share a divisor of 120, giving 16:9.
Resizing without stretching
To keep proportions when resizing, multiply the new width by the original height and divide by the original width:
new height = new width × original height ÷ original width
For example, a 1920 × 1080 image resized to 1280 wide becomes 1280 × 1080 ÷ 1920 = 720 pixels high.
Common ratios and where they are used
- 16:9: HD and 4K video, most monitors and TVs
- 9:16: vertical video for stories, reels and shorts
- 4:3: older displays, many tablets and presentation slides
- 1:1: square social posts and profile pictures
- 4:5: portrait posts in social feeds
- 21:9: ultrawide monitors and cinema
Dimensions that do not divide evenly produce long ratios such as 683:384. That is normal, and the decimal value is often easier to compare.
Frequently asked questions
How do I calculate an aspect ratio?
Divide the width and height by their greatest common divisor. For 1920 × 1080 that divisor is 120, giving 16:9.
What size is 16:9?
Any size where the width divided by the height is about 1.778. Common examples are 1280 × 720, 1920 × 1080, 2560 × 1440 and 3840 × 2160.
Why does my ratio look strange, like 683:384?
Some resolutions are not an exact match for a simple ratio. 1366 × 768 is very close to 16:9 but not exact, so the reduced ratio is long.
Can I use decimals?
Yes. Decimal inputs work, and the new dimensions are rounded to two decimal places.
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