About Dimensions
Dimensions measures space the quick way. Activate it with Alt+D, then move the pointer and it shows the distance up, down, left and right until it hits a border, so you can read the gap between two elements in pixels. Felix Niklas made it, and it is MIT licensed with the source on GitHub.
Because it reads pixels rather than the page's structure, it works on anything you can see: buttons, icons, images, videos, and a mockup PNG or JPEG you drop into the browser. Holding Alt measures a connected area, which is handy for the radius of a circle. It is tiny, under 20 KB in Chrome, and its Chrome manifest asks only for the active tab and scripting permissions.
It is a measuring tape, not an inspector. It does not read CSS, and the listing says it does not work well on images, where colours change from pixel to pixel. The Chrome build moved to Manifest V3 in October 2025, while the Firefox build on the store dates from April 2024. Chrome's listing says no data is collected, and the rating is 4.0 from about 460 ratings. If you want a free, small, readable ruler, install it.
Pros and cons
- Measures up, down, left and right to the nearest border
- MIT licensed with public source
- Tiny and asks only for active tab and scripting
- Works on dropped-in mockup images too
- Reads pixels, not CSS
- Poor on photographs and gradients
- Firefox build last updated in April 2024
Permissions
In Chrome it asks only for activeTab and scripting, so it runs on the page where you trigger it. The Firefox build asks for access to all sites.
