What is an aspect ratio?

An aspect ratio is the proportional relationship between a width and height, expressed as W:H. For example, 1920×1080 pixels simplifies to a 16:9 aspect ratio, which is the standard for HD and 4K video.

How do I calculate a missing dimension from an aspect ratio?

Enter the known dimension (width or height) and select or type the desired aspect ratio. The calculator will compute the missing dimension automatically while preserving the ratio.

What is the most common aspect ratio for video?

16:9 is the standard for HD and 4K video (YouTube, TV, monitors). 9:16 is used for vertical video (Instagram/TikTok Stories). 21:9 is the ultrawide cinematic format.

How does the resolution comparison mode work?

Enter two width×height pairs. The tool calculates both aspect ratios, tells you whether they match, and shows the scale factor — how many times larger or smaller one resolution is relative to the other.

Aspect Ratio Calculator

Calculate aspect ratios, find missing dimensions, and compare resolutions. Works instantly in your browser — no upload, no account.

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Calculate Ratio from Dimensions

Width (px)

Height (px)

Aspect Ratio16:9

Decimal Ratio1.7778

Width as % of Height177.78%

Matches Standard16:9

Ratio from Dimensions

Enter any width and height to instantly get the simplified aspect ratio.

Find Missing Dimension

Know one side and the ratio? Calculate the other dimension in one click.

Compare Resolutions

Compare two resolution pairs to see if they share the same aspect ratio and calculate the scale factor.

Common Ratio Library

Quick-select from 9 standard aspect ratios: 16:9, 4:3, 1:1, 9:16, 21:9, and more.

Aspect Ratio Calculator

Frequently Asked Questions

What is an aspect ratio?

How do I find a missing dimension?

What is the most common video aspect ratio?

What does the scale factor mean in comparison mode?