MotionShine01 / Enter
Type a size
Enter a width and height, or pick an image or video to read its size.
Free tool
Aspect ratio calculator.
Find the aspect ratio of a size, an image or a video, and work out a new width or height that keeps the same shape. Useful before you resize a recording for YouTube, a phone or a slide.
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Keep a ratio, change the size
This is arithmetic in your browser. A file you pick is only read for its size and never uploaded.
How it works
Three steps, nothing to install.
02 / Read
See the ratio
The page shows the ratio, such as 16:9, and its decimal value.
03 / Resize
Keep the shape
Pick a ratio and type a new width or height. The other side is worked out for you.
Questions
Good to know.
What is an aspect ratio?
The shape of a picture: its width compared with its height. 1920 x 1080 and 1280 x 720 are both 16:9, because the width is 16/9 times the height.
Why does my size not give a neat ratio?
Some sizes, such as 1366 x 768, do not reduce to small whole numbers. The page then says which common ratio it is closest to.
Which ratio should a video be?
16:9 suits YouTube and most screens, 9:16 suits Reels, TikTok and Shorts, 1:1 and 4:5 suit feed posts. Mac screens are often 16:10.
Why are the sizes in the table even numbers?
Most video encoders need even widths and heights, so the heights are rounded to the nearest even number.
How do I change the ratio of a video?
Use the video resizer to fit it into a new shape with bars, or the crop tool to cut it to that shape.
Is my file uploaded?
No. The page only reads its width and height in your browser.