Toolrack

Aspect Ratio Calculator

Works offlineNothing is uploadedFree, no sign-up
Aspect ratio—
As a decimal—
Common name—
Megapixels—

Resize keeping the ratio

Type a new width or height — the other side follows the ratio.

Fit into a box

The size your image becomes inside a frame — thumbnail, slide, or screen.

Work out an image or video's aspect ratio, resize it without distortion, and fit it into any box — with the real names screens use, so 3440×1440 says "21:9" and 1080×1350 says 4:5 portrait.

The ratios in circulation

RatioWhere it lives
16:9TV, YouTube, laptops — the default of the age
9:16stories, reels, TikTok — 16:9 turned upright
4:3older screens, iPads, most compact cameras
3:2DSLR and mirrorless sensors, 10×15 cm prints
1:1profile pictures, album covers, feed posts
4:5portrait feed posts — the most screen a photo gets on a phone
21:9ultrawide monitors — really 43:18 or 64:27
1.85:1 / 2.39:1cinema flat and anamorphic scope

Everything runs locally in your browser and works offline once loaded.

Frequently asked questions

What is an aspect ratio?

The proportion between an image's width and height, written as two numbers: 16:9 means 16 units across for every 9 down. It says nothing about actual size — 1280×720 and 3840×2160 are both 16:9 — which is exactly why it matters: content keeps its shape across screens of every size, as long as the ratio is respected.

How do I resize without stretching or squashing?

Change both sides by the same factor. This page does the arithmetic: enter the original size, then the one new dimension you know, and the other is computed from the exact ratio and rounded once at the end. Distortion happens when width and height are rounded separately at intermediate steps, or one side is simply guessed.

Why does the tool say my "21:9" monitor isn't 21:9?

Because none are. 3440×1440 reduces to 43:18 (2.389:1) and 2560×1080 to 64:27 (2.370:1) — "21:9" (2.333:1) is a marketing name that no shipping panel matches exactly. The tool shows the true reduced ratio and still recognises the family name, so both statements are available: the exact one and the one people search for.

What is the difference between contain and cover?

Two answers to the same mismatch. Contain scales the image until it fits entirely inside the box, leaving empty bands on one axis — nothing is lost, letterboxing appears. Cover scales it until the box is entirely filled, cropping whatever overflows — no bands, but edges are cut. They are the CSS object-fit values of the same names, and every thumbnail system chooses one.

Which ratios should I use for social media?

The safe set in 2026: 1:1 and 4:5 for feed posts (4:5 gets the most screen area on phones), 9:16 for stories, reels and TikTok, 16:9 for YouTube and link previews. Platforms crop anything else to their nearest supported ratio, so exporting at the target ratio is the only way to control what survives.

Does rounding to whole pixels break the ratio?

Microscopically, and unavoidably — 1000 wide at 16:9 is 562.5 tall, and half pixels do not exist. This page rounds exactly once, at the final result, keeping the error under half a pixel. That is well inside the 1% tolerance the ratio matcher uses, and invisible in practice; video encoders additionally want even dimensions, which is worth knowing if a tool rejects an odd height.

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