720px

720px refers to a width of 720 CSS pixels. In web design and image production, px is a CSS pixel, an abstract unit that can map to different numbers of device pixels depending on the device's pixel ratio. Therefore, a 720px wide element may render larger or smaller in physical size on different screens, even when the CSS width is fixed.

In responsive design, 720px is a common breakpoint or content width. Web designers may structure layouts so that elements stack or reflow when the viewport is at least 720px wide or narrower than that. Breakpoints at or around 720px are often paired with larger thresholds like 768px or 1024px to accommodate tablets and mobile devices.

720p is unrelated but commonly conflated. 720p denotes a video resolution of 1280×720 pixels with a 16:9 aspect ratio and is widely used as the standard HD format. The term 720px should not be treated as a video resolution, though an image or video element might be sized to 720px wide in CSS.

Practical considerations: for images and media, serving content at approximately 720px wide can optimize loading on many mobile devices; using responsive techniques such as srcset and sizes for images or CSS max-width: 100% can keep content fluid while maintaining quality across devices. Common CSS queries include @media (min-width: 720px) and @media (max-width: 720px).