Aspect Ratio Calculator – Resize Width and Height While Keeping Proportions

Use this free aspect ratio calculator to resize dimensions while maintaining the original proportions. Enter your starting width and height, then input either the target width or height to auto-calculate the other. Instantly compare sizes visually and export pixel-perfect results.

How This Aspect Ratio Calculator Works

This interactive aspect ratio calculator was custom-built using vanilla JavaScript, HTML5, and PHP as a WordPress shortcode. It helps users resize dimensions accurately while maintaining proportional values. Whether you're designing responsive layouts, editing media, or preparing print assets, this tool simplifies aspect ratio calculations and visual comparisons.

Technologies Used

PHP (WordPress Shortcode): The calculator is embedded as a shortcode using a custom PHP function, making it reusable across posts and pages.
HTML5 + CSS3: The markup includes semantic tags, accessible labels, and a responsive layout with fieldsets, labels, and form controls optimized for usability.
JavaScript (No Libraries): Pure JavaScript handles the calculator logic, visual rendering, and live updates without relying on frameworks.

Key Features

Unit Conversion: Supports conversions between multiple units including px, in, cm, mm, pt, ft, vw, vh, em, and rem. When a unit changes, the calculator preserves the true dimension using a custom conversion logic.
Auto-Calculation: Enter either width or height to have the other value automatically computed while maintaining the selected aspect ratio.
Dynamic Visual Preview: Both original and resized dimensions are rendered side-by-side in a real-time, scaled comparison. Dimensions are labeled using floating elements (e.g., 800px × 300px) that update instantly with input.
Debounced Input Handling: The calculator uses a debounce function to optimize performance and avoid excessive calculations as users type.

Why Build with Vanilla JavaScript?

This project was created without any libraries like React or jQuery. By using vanilla JavaScript, the tool remains lightweight and loads fast, while also being easier to integrate into any WordPress-based website. It’s proof that you can build highly dynamic tools using only the web platform’s core technologies.

Use Cases

Designing responsive web components
Resizing images for blog posts or featured thumbnails
Adjusting embedded videos while keeping a consistent aspect ratio
Creating pixel-perfect UI mockups with unit conversion

Try the calculator above by entering your dimensions and selecting any unit — it’s designed for precision, speed, and flexibility.