What is an Aspect Ratio Calculator?
An aspect ratio calculator helps you find the proportional relationship between the width and height of an image, video, or screen. For example, a 1920×1080 pixel video has an aspect ratio of 16:9. Knowing this ratio is essential when resizing media so it does not appear stretched or squished — you scale dimensions while keeping the ratio constant.
Graphic designers use it to prepare banner ads at exact sizes, video editors use it to crop footage for YouTube (16:9) or Instagram Reels (9:16), and web developers use it to embed responsive iframes. Architects and engineers use aspect ratios when scaling blueprints. Our tool handles both directions: find the ratio from known dimensions, or calculate a missing dimension from a known ratio.
How to Use the Aspect Ratio Calculator
- Calculate ratio from dimensions: Enter the width and height of your image or screen — the simplified ratio (e.g. 16:9) and decimal value appear instantly.
- Scale dimensions: Enter your ratio (e.g. 16 and 9), choose whether you know the width or height, enter the known value, and get the matching dimension.
- Use the common presets (16:9, 4:3, 1:1, 21:9, 9:16, 3:2…) to load popular ratios instantly.
- Copy the result and use it in your design software, CSS, or video editor.
Why Use Our Aspect Ratio Calculator?
- 100% Free — No subscriptions or watermarks on results.
- No Registration — Open and use immediately without signing up.
- Browser-Based — Runs client-side; works offline once loaded.
- Common Presets — One-click loading of 16:9, 4:3, 1:1, 21:9, 9:16 and more.
- Bidirectional — Calculate from dimensions or from a ratio — both directions supported.
Frequently Asked Questions
YouTube recommends 16:9 (widescreen) for standard uploads. Common resolutions include 1920×1080 (Full HD), 2560×1440 (2K), and 3840×2160 (4K). All share the same 16:9 ratio.
4:3 is the older "standard" TV ratio — almost square. 16:9 is the modern widescreen ratio used by most HDTVs, monitors, and online video platforms. 16:9 is wider relative to its height, giving a more cinematic feel.
Use the CSS property aspect-ratio: 16 / 9; on modern browsers. Alternatively, set a percentage-based padding-bottom trick: for 16:9, use padding-bottom: 56.25% on a wrapper element with position: relative.
Instagram supports multiple ratios. Square posts use 1:1, portrait posts use 4:5 (recommended for feed), landscape posts use 1.91:1, and Reels/Stories use 9:16. Use our presets to calculate the correct dimensions for each format.