---
title: "Aspect Ratio Calculator - Resize Proportions | CanDoYa"
description: "Aspect ratio calculator for images, video and layouts. Reduce width:height, get CSS aspect-ratio, and calculate matching resize dimensions."
url: https://candoya.com/tools/aspect-ratio-calculator/
locale: en
type: browser-tool
---

# Aspect Ratio Calculator

Category: Calculators

## What is an aspect ratio calculator?

An aspect ratio calculator reduces a width and height to the simplest width:height relationship, such as 1920 x 1080 becoming 16:9. It also calculates the missing resized dimension so images, videos and layout boxes keep the same proportions.

Enter any source width and height. The calculator reduces the ratio, shows the decimal width divided by height, labels the orientation, and gives a copyable CSS `aspect-ratio` value. Add either a target width or target height to resize proportionally without stretching.

## How to use it

1. **Enter source dimensions** - Type the original width and height in pixels or any matching unit.
2. **Read the reduced ratio** - The tool simplifies the pair to the smallest width:height ratio and shows the decimal value.
3. **Resize proportionally** - Enter a target width or target height. The missing dimension is calculated from the same ratio.
4. **Copy the CSS** - Use the CSS aspect-ratio value in responsive layouts, cards, embeds or media containers.

## Who it's for

- **Designers** checking whether an image is 16:9, 4:3, 3:2, square or portrait before placing it in a layout.
- **Developers** copying a clean CSS `aspect-ratio` declaration for cards, embeds and responsive media.
- **Video editors** resizing thumbnails and frames while keeping the original proportions.
- **Photographers** scaling camera images for web export without distortion.

## Expert note

For integer pixel dimensions, the exact reduced ratio comes from the greatest common divisor. Decimal dimensions are still useful for proportional resizing, but camera and video formats usually reduce cleanly from integer pixel sizes.

## Frequently asked questions

### How do you calculate aspect ratio?

Divide the width and height by their greatest common divisor. For example, 1920 and 1080 share a divisor of 120, so 1920:1080 reduces to 16:9.

### How do I resize without changing aspect ratio?

Use one known target dimension and multiply or divide by the ratio. If you know the target width, height equals target width multiplied by original height divided by original width.

### What is the CSS aspect-ratio value?

CSS uses a slash form such as aspect-ratio: 16 / 9;. The calculator shows the reduced pair so you can copy it directly into a rule.

### Can I use units other than pixels?

Yes. The ratio is unitless, so width and height can be pixels, inches, millimeters or any matching unit. The resize result uses the same unit you typed.

### Is this aspect ratio calculator private?

Yes. All calculations run locally in your browser. No image, video or dimension data is uploaded.

## Related tools

- [Percentage Calculator](https://candoya.com/tools/percentage-calculator/)
- [Fraction Calculator](https://candoya.com/tools/fraction-calculator/)
- [Perimeter Calculator](https://candoya.com/tools/perimeter-calculator/)
- [CSS Clamp Calculator](https://candoya.com/tools/css-clamp-calculator/)
- [Ratio Calculator](https://candoya.com/tools/ratio-calculator/)

---

*Markdown edition of <https://candoya.com/tools/aspect-ratio-calculator/>, published for AI agents and other automated readers. Index of key pages: <https://candoya.com/llms.txt>.*