The Extension has been updated to manifest v3, the older version of the extension (v2) https://chromewebstore.google.com/detail/dimensions/baocaagndhipibgklemoalmkljaimfdj This extension measures the dimensions from your mouse pointer up/down and left/right until it hits a border. So if you want to measure distances between elements on a website this is perfect. It doesn't really work with images because there the colors change a lot pixel to pixel. Images & HTML Elements Measure between the following elements: images, input-fields, buttons, videos, gifs, text, icons. You can measure everything you see in the browser. Mockups Your designer handed you mockups as PNGs or JPEGs? Just drop them into Chrome, activate Dimensions and start measuring. Keyboard Shortcut You can start and stop dimensions with the ALT + D shortcut. Area Boundaries Wanna get the radius of a circle? Is text standing in your way? Press Alt to measure the dimensions of a connected area. Open Source Dimensions is Open Source and hosted on Github. Want to port it to Firefox? Go ahead and fork it. Pull requests are welcome! https://github.com/mrflix/dimensions