Aspect Ratio Calculator — Free Online Image & Video Ratio Calculator

Aspect Ratio Calculator — Free Online Image & Video Ratio Calculator. Free online aspect ratio calculator. Calculate image aspect ratios, find missing dimensions, convert between ratios, and resize for 16:9, 4:3, 21:9 and more.

Use our free aspect ratio calculator to instantly find the aspect ratio of any image or video, calculate missing dimensions, and resize to any target resolution.

Whether you need a ratio calculator for 16:9 HD video, 4:3 standard screens, 21:9 ultrawide, or a custom image ratio calculator for responsive web design, our tool handles it in real time — no signup required.

Enter any two dimensions to see the simplified ratio, or lock one side and compute the other. Runs 100% in your browser — private and instant. Related: QR Code Generator, SVG Placeholder Generator.

Our image aspect ratio calculator covers every common display format — 16:9 (HD/4K), 4:3 (classic monitors), 21:9 (ultrawide cinema), 1:1 (square social), 9:16 (portrait/mobile), 3:2 (DSLR/SLR).

Use the calculate aspect ratio feature to verify your photo crops meet platform requirements for YouTube thumbnails (16:9), Instagram posts (1:1 or 4:5), or Twitter cards (2:1).

The aspect ratio converter section lets you lock either the width or height and instantly compute the other dimension for any ratio. Perfect for video editors, web designers, photographers, and developers who need precise aspect ratio dimensions.

Frequently asked questions

How do I calculate the aspect ratio of an image or video?

Type the pixel width and height into the Width and Height fields of the Calculate Ratio from Dimensions section. The Aspect Ratio box shows the simplified ratio right away, for example 1920 x 1080 becomes 16:9 and 800 x 600 becomes 4:3.

How do I find the missing width or height for a ratio?

In Calculate Dimensions from Ratio, set Ratio Width and Ratio Height or click a Common Ratios preset. Select Lock Width to type a Target Width and get the height, or Lock Height to type a Target Height and get the width. The computed side is rounded to the nearest whole pixel.

What is 16:9 in pixels?

Common 16:9 sizes are 1280 x 720, 1920 x 1080, 2560 x 1440 and 3840 x 2160. For any other size, click the 16:9 preset, keep Lock Width selected and type your width; the matching height appears in Target Height.

Which aspect ratio presets are available?

One-click presets are provided for 16:9 (HD and 4K video, YouTube), 4:3 (classic monitors), 21:9 (ultrawide), 1:1 (square posts), 9:16 (vertical phone video) and 3:2 (many camera photos). You can also type any custom ratio into the ratio fields.

Why does my screen resolution show an odd ratio like 683:384?

The calculator divides both numbers by their greatest common divisor and does not round to the nearest named ratio. Resolutions such as 1366 x 768 are not exactly 16:9, so they reduce to 683:384. Compare the result with the presets to see which standard ratio it is closest to.

How to use this online tool

Aspect Ratio Calculator — Free Online Image & Video Ratio Calculator is designed for fast browser workflows when you need to format, validate, convert, decode, encode, generate, or inspect data without opening a heavy desktop app. Start with the input field or visible options, review the result, then copy or download the output for the next step.

Private processing in your browser

Aspect Ratio Calculator — Free Online Image & Video Ratio Calculator keeps the normal processing step local in your browser. That is useful for code snippets, tokens, documents, configuration values, text samples, and other material that should not be sent to a remote service unless you explicitly choose to share it.

When this tool is useful

Use Aspect Ratio Calculator — Free Online Image & Video Ratio Calculator for repeatable developer tasks, technical documentation, QA checks, quick conversions, debugging, content cleanup, and internal team workflows. The page focuses on clear inputs, immediate feedback, and output that is easy to reuse in code, reports, tickets, emails, or notes.

Practical tips

Before copying the final result, check important details such as spacing, casing, filenames, encoding, token structure, line breaks, or output format. Small checks prevent mistakes when the result is reused in source code, API requests, documentation, spreadsheets, or shared files.