Apple showed off a brand new app during WWDC called Measure, which can measure any real-world object just by using your iPhone’s camera.
The company provided a very brief demo on how it works, and it looks be fairly easy to use—just point your iPhone at an object, line up the dot on the screen to where you want your measurement to begin and end, and you’ll instantly being given its measurement.
You can also scan something like a photo (for example) and it will give you the dimensions of it.
The app uses Apple’s ARKit software technology, and while there are similar apps that already exist in the App Store (like Tape Measure, for instance), Apple’s own Measure app seems to be a simpler and better option.
Nothing else was mentioned about the new Measure app (including whether or not it will be a default app), but we can assume it’ll be available once iOS 12 is released, regardless.