Aspect Ratio Calculator

Calculate, resize, and compare image or video aspect ratios. Get CSS output instantly.

Last reviewed: April 2026
Reviewed by , software engineer · last updated April 2026

New to this tool? Click here for instructions

Enter width and height above to calculate the aspect ratio.

How to Use the Aspect Ratio Calculator

The Aspect Ratio Calculator is a free online tool that helps you calculate, resize, and compare aspect ratios. To use it, simply enter the width and height of an image or video, and the calculator will provide the simplified aspect ratio, orientation, CSS value, and megapixel count. You can also use the Resize mode to calculate missing dimensions when you know one dimension and the aspect ratio. Enter the width and height of an image or video. The calculator will provide the simplified aspect ratio, orientation, CSS value, and megapixel count. Use the Resize mode to calculate missing dimensions.

When to Use the Tool in Real Workflows

The Aspect Ratio Calculator is ideal for web and graphic designers who need to maintain the correct aspect ratio for images, videos, and containers. It's also useful for developers who need to ensure that their responsive layouts are correctly maintaining aspect ratios. Additionally, it's helpful for anyone who needs to convert dimensions or compare aspect ratios for various projects.

How It Works

The Aspect Ratio Calculator uses a simple formula to calculate the aspect ratio. The formula is the width divided by the height. The calculator then simplifies the ratio to its lowest terms, providing a more readable format. The tool also provides the CSS aspect-ratio property, which can be directly copied into your stylesheet to maintain the correct aspect ratio.

Tips, Edge Cases, or Limitations

When using the Aspect Ratio Calculator, make sure to enter the dimensions in pixels. The calculator does not support fractional dimensions. Additionally, the tool assumes that the aspect ratio is a whole number ratio. If you need to work with non-whole number ratios, you may need to manually simplify the ratio before entering it into the calculator.

Frequently Asked Questions

An aspect ratio is the proportional relationship between the width and the height of a rectangle. It is written as two integers separated by a colon, such as 16:9 or 4:3.
The CSS aspect-ratio property lets you define a box's ratio without JavaScript or the old padding-top trick. For example, aspect-ratio: 16 / 9; maintains 16:9 as width changes.
To calculate a new height given a width and aspect ratio, divide the width by the aspect ratio. For example, if the width is 1920 pixels and the aspect ratio is 16:9, the height would be 1080 pixels.
The best aspect ratio for YouTube videos is 16:9. This is the universal widescreen standard and is used by most video platforms.
The 4:3 aspect ratio is the classic TV and CRT monitor standard, while the 16:9 aspect ratio is the universal widescreen standard. The 16:9 ratio is more common in modern displays and video content.

Quick reference

Aspect Ratio Calculator Quick Reference
Aspect Ratio Width Height Common Use
16:9 1600 900 HDTV, gaming monitors
4:3 1280 768 Older TVs, projectors
21:9 2100 900 Cinema displays, ultrawide monitors
1:1 1024 1024 Square images, social media posts
3:2 1920 1280 Photography, some cameras
18:16 1800 1600 Smartphone screens, vertical video

Example walk-through

Worked example: step-by-step

Step 1. Navigate to the Aspect Ratio Calculator webpage and locate the input fields for width and height measurements.

Step 2. Enter the desired dimensions (e.g., width: 1920, height: 1080) into the respective fields.

Step 3. Click the "Calculate" button to process the input, which will simplify the ratio by dividing both values by their greatest common divisor (GCD).

Step 4. Review the output display showing the simplified aspect ratio (e.g., 16:9) and optional adjustments for target ratios like 4:3 or 1:1.


// Sample input
width = 1920
height = 1080

Step by step, the tool computes GCD(1920, 1080) = 120, then divides both values to produce the final ratio.


// Expected output
Simplified Aspect Ratio: 16:9