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Aspect Ratio Calculator

Find proportional width and height for any aspect ratio instantly

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An aspect ratio calculator finds the missing width or height that keeps your video or image proportional to a target ratio such as 16:9, 9:16, 4:3, or 1:1. Enter one known dimension and the desired ratio, and ClipTools instantly returns the matching dimension so nothing stretches or gets cropped. It also works in reverse: type in any width and height, and it reduces them to a simplified ratio like 1920x1080 to 16:9.

Because this is a pure math tool, the calculation runs entirely in your browser using plain JavaScript with no file upload, no signup, and no waiting. There is nothing to process on a server, so results appear the instant you type. It is built for video editors, social media managers, web designers, and photographers who need correct dimensions for YouTube, Instagram Reels, TikTok, ad banners, or print before they ever open an editor.

Why use this tool

Instant, no-upload math

Calculations run in plain JavaScript on your device, so there is no file to upload and results appear the moment you type, with nothing sent to a server.

Works in both directions

Find a missing width or height from a ratio, or enter two dimensions to reduce them to a simplified ratio like 16:9, covering both common workflows in one tool.

Ready-made platform presets

One-click presets for 16:9, 9:16, 4:3, 1:1, 21:9, and more map directly to YouTube, Reels, TikTok, square posts, and cinematic formats so you skip the guesswork.

Prevents stretching and black bars

By giving you the exact proportional dimensions before you export, it helps you avoid distorted video, unwanted cropping, and letterboxed black bars.

How to use the Aspect Ratio Calculator

  1. Pick a target ratio

    Select a preset aspect ratio such as 16:9, 9:16, 4:3, or 1:1, or type your own custom ratio like 21:9.

  2. Enter your known dimension

    Type in the width or height you already have, for example a width of 1920 pixels.

  3. Read the calculated dimension

    The tool instantly fills in the proportional missing value, such as a height of 1080 for a 16:9 ratio.

  4. Reverse it to find a ratio

    Alternatively, enter both a width and height to have the calculator reduce them to a simplified aspect ratio.

  5. Apply the dimensions

    Copy the calculated numbers into your editor, exporter, or the ClipTools Change Resolution tool to resize your video.

Popular use cases

  • A video editor preparing a YouTube upload enters 1080 as the height with a 16:9 preset to confirm the matching 1920 width before exporting.
  • A social media manager repurposing a landscape clip for Instagram Reels checks the 9:16 dimensions, like 1080x1920, to avoid awkward cropping.
  • A web designer sizing a hero banner enters a fixed container width and a 21:9 ratio to get the exact height needed for a consistent layout.
  • A photographer with a 6000x4000 image uses the reverse mode to confirm it is a 3:2 ratio before sending it to print.

Frequently asked questions

Is the aspect ratio calculator free to use?
Yes, the ClipTools aspect ratio calculator is completely free with no signup, account, or usage limits. You can calculate as many dimensions and ratios as you want at no cost.
Do I need to upload a file to calculate an aspect ratio?
No. This is a pure math calculator, not a file converter, so there is nothing to upload. You only type in numbers (a width, height, or ratio), and the result is computed instantly in your browser. No video or image ever leaves your device.
How does the calculator keep my dimensions private?
All calculations run locally in your browser using plain JavaScript. No dimensions, files, or data are sent to any server, so your inputs stay entirely on your own device. There is no network request involved in the math at all.
What aspect ratios does it support?
It supports any ratio you enter, including common presets like 16:9 (YouTube and HD video), 9:16 (Reels, Shorts, TikTok), 4:3 (classic and some cameras), 1:1 (square Instagram posts), 21:9 (cinematic ultrawide), and 3:2 (photography). You can also type a custom ratio such as 2.39:1.
Can it calculate the aspect ratio from a width and height I already have?
Yes. Enter both dimensions, for example 1920 and 1080, and the tool reduces them to the simplest whole-number ratio, in this case 16:9. This is useful for identifying the ratio of an existing video or image file.
Will this calculator resize or crop my actual video or image?
No. It only calculates the correct numeric dimensions; it does not modify any media. To physically resize a video, use the ClipTools Change Resolution tool, and to crop it, use the Video Cropper, both of which process files locally in your browser.
Why does my calculated height come out as a decimal?
Some ratio and dimension combinations do not divide into whole pixels, so the math produces a fraction. For video encoding, round to the nearest even number, since most codecs like H.264 require width and height to be divisible by 2.
How fast is the calculation?
It is instant. Because the math runs in plain JavaScript on your device with no upload or server round trip, the proportional dimension appears the moment you enter your numbers.

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