Calculate Image Dimensions for Web

If your CSS container is 800px wide and you want a 16:9 image, calculate the height: 800 / 16 × 9 = 450px. This tool does that for you.

Using aspect-ratio CSS? The tool shows the simplified ratio (e.g. 8:5) which you can use directly in aspect-ratio: 8/5 in CSS.

For responsive images, calculate at your largest breakpoint, then CSS handles the scaling. The ratio stays the same at all widths.

Always specify width and height attributes on <img> tags (matching the image's natural ratio) to prevent Cumulative Layout Shift (CLS).