Converting a photo or video to a different aspect ratio — say, a widescreen shot into a vertical Instagram Story format — means cropping it precisely, and figuring out the exact pixel dimensions to crop to by hand involves a bit of ratio math.
This tool takes your source media's width and height, along with a target aspect ratio, and calculates the largest possible crop dimensions that fit within your original media while matching the target ratio exactly.
It's useful for preparing the same source image or video for multiple platforms with different aspect ratio requirements — square for one platform, vertical for another — without guessing at crop dimensions in an editor.
Because everything runs locally in your browser, results appear instantly and nothing you type or upload is ever sent to a server.
Bookmark this page if you expect to use this tool regularly — it loads fast and behaves the same way every time, with no account needed.
This kind of task shows up constantly in everyday writing, coding, design, and admin work, which is exactly why a dedicated, focused tool saves so much back-and-forth.
A tool that does one job well, without a cluttered interface or unrelated features competing for attention, tends to be faster to use than a heavier all-in-one app.
If you find yourself needing this conversion or calculation often, keeping this page open in a tab is usually faster than digging through a bigger software suite's menus.
Frequently asked questions
Does this crop the actual file, or just tell me the dimensions?
This calculates the exact dimensions needed; you'd apply that crop using an image or video editor, or the crop tool elsewhere on this site for images.
What if my source is smaller than the calculated crop?
The calculator always fits the crop within your source dimensions, so the result never exceeds your original media's size.