Element Size Ruler от Guerra

Element Size Ruler allows you to measure element sizes and distances on any webpage with a simple, user-friendly ruler. Activate the extension with a toolbar button and start measuring by clicking and dragging on the page. The ruler updates in real-time to show width, height, and coordinates.

Features:
Measure element sizes in pixels
Real-time updates of width, height, and coordinates
Toggle activation with a toolbar button
Supports mouse and touch input