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Aspect Ratio Calculator

Enter a width and height to see the simplified aspect ratio, then type a new width or height to get the other dimension that keeps the exact same ratio. Pure math, runs in your browser, no upload.

Aspect ratio

16:9

Decimal

1.7778

Solving with ratio: 16:9

New height: —

New width: —

Type a width to get the matching height, or a height to get the matching width — both stay in the same ratio.

How to use it

  1. 1Type your original width and height — the simplified ratio (like 16:9) appears instantly.
  2. 2Prefer a standard ratio? Tap a preset such as 16:9, 9:16, 4:3, 3:2, 1:1 or 21:9 to solve against it instead.
  3. 3In the resize section, enter a new width to get the matching height (or a new height to get the matching width) — everything stays in proportion.

Aspect ratio describes the relationship between a frame’s width and its height, written as two numbers like 16:9. It stays the same no matter the pixel count: 1920×1080, 1280×720 and 3840×2160 are all 16:9. This calculator finds that simplified ratio for you using the greatest common divisor, so any size collapses to its cleanest form.

16:9 is the default for desktop video, YouTube and most screen recordings — it matches modern monitors and looks right on TVs and laptops. When you need vertical content for TikTok, Instagram Reels or YouTube Shorts, you switch to 9:16, which fills a phone screen held upright. Picking the wrong one early means letterboxing or awkward cropping later, so it pays to decide before you record.

Other ratios still matter. 1:1 is the classic square for Instagram feed posts and profile-style clips. 4:3 is the older “classic” TV and early-webcam shape, still handy for slide decks and some app UIs. 3:2 comes from photography, and ultrawide 21:9 suits cinematic edits and wide desktop captures. Whatever the target, the goal is to lock the ratio first, then choose exact pixel dimensions that fit it.

Because the tool keeps the ratio fixed while you resize, you can safely scale a project up or down. Set the ratio to 16:9, type a new width of 1280, and you instantly get 720 for the height — no distortion. That is the same logic editors use when exporting: keep the aspect ratio constant so nothing gets stretched, and only the resolution changes.

FAQ

What is an aspect ratio?
It is the proportion between width and height, written as width:height. 16:9 means for every 16 units of width there are 9 of height. The same ratio can be any resolution — 1920×1080 and 1280×720 are both 16:9.
What aspect ratio should I use for TikTok, Reels or Shorts?
Use 9:16, the vertical full-screen ratio (for example 1080×1920). It fills a phone held upright and is what TikTok, Instagram Reels and YouTube Shorts expect. For desktop video and YouTube’s main feed, use 16:9 instead.
How do I resize an image or video without stretching it?
Keep the aspect ratio fixed and change only one dimension, then let the other follow. Set your ratio here, type the new width, and the calculator gives the height that keeps the same proportion so nothing gets distorted.
What is the difference between 4:3 and 16:9?
4:3 is the older, more square “classic” shape used by old TVs, many slide decks and some app screens. 16:9 is wider and is today’s standard for monitors, YouTube and most screen recordings.
Is my data uploaded anywhere?
No. This is pure math that runs entirely in your browser — there is no image or file upload and nothing is sent to a server.

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