Aspect Ratio Calculator

📖 Tool Introduction

The Aspect Ratio Calculator is a free online tool built for designers, front-end developers and content creators, and it solves the ratio conversions that keep coming up in everyday design work. It offers two complementary directions. In the first, when you have the pixel size of an image or a canvas, such as 1920 by 1080, you enter the width and height, and the tool reduces that size to its cleanest ratio using the greatest common divisor, giving you 16:9 together with the decimal value of width divided by height. In the second, when you have already settled on a target ratio such as 16:9 and you know only one side, say a width of 1280 pixels, the tool automatically works out how many pixels the other side should be. Along the top there are eight built-in quick presets for 16:9, 4:3, 1:1, 3:2, 9:16, 21:9, 2:3 and 5:4, so a single tap fills the ratio width and height and saves you typing. Whether you are cropping an image, setting a cover size, arranging a slide deck or planning a video frame, you get an accurate answer in an instant. Every calculation runs locally in your browser, nothing is uploaded, and the interface is available in Simplified Chinese, Traditional Chinese and English, working equally well on a phone or a computer. The whole point of the tool is to remove mental arithmetic from your workflow, so you can stay focused on layout and composition rather than grabbing a calculator and counting factors by hand. Because the two cards sit side by side, you can reduce a real size and reverse a target ratio in the same session, which makes it easy to check that the dimensions you are about to hand to an export pipeline actually match the ratio your design calls for.

✨ Key Features

• Reduce size to ratio: uses the Euclidean greatest common divisor to turn any pixel size into the simplest integer ratio
• Reverse-calculate size: given a ratio and any one side, it works out the exact missing pixel length
• Eight common presets: widescreen, standard, square, portrait and ultra-wide filled in one tap
• Decimal and divisor shown: displays both the width-over-height decimal and the GCD used for reduction
• One-click copy: results from both directions can be copied together for notes in a document or design file
• Friendly empty handling: empty or invalid input triggers a clear hint instead of a wrong number

📝 How to Use

1. To reduce a ratio, enter the width and height pixels of an image or canvas in the top card
2. Click the reduce button and read the simplest ratio, the decimal value and the greatest common divisor
3. To reverse-calculate a size, type the ratio width and height in the bottom card, or tap a preset at the top
4. Choose width-to-height or height-to-width, then type the known side length in pixels
5. Click compute the other side, and copy the result for later use

⚠️ Notes

• Positive input: width, height and side length must all be numbers greater than 0; invalid input gives a friendly hint
• Rounding rules: the reduced ratio is an integer, while the reverse-calculated side keeps two decimals for precision
• Ratio direction: 16:9 is landscape and 9:16 is portrait, so mind the order of width and height
• Frame of reference: the presets cover common screen and camera scenarios; special frames still need your own math
• Fully local: every conversion happens in the browser with no network request, so your data stays safe