Apple's App Measure uses AR to measure anything with your iPhone.
Apple showed a new app during WWDC called Measure, which can measure any real object using your iPhone's camera.
The company has provided a short demo on how it works, and it seems easy enough to use - just point your iPhone at an object, align the dot on the screen to where you want to start and end the measurement, and its measurement is given. .
You can also scan something through a photo (for example) and it will give you the size of the object represented.
The app uses software technology ARKit on Apple, and while there are similar apps already in the App Store (like Tape Measure, for example), Apple's Measure app seems to be a simpler and better option.
Nothing else has been mentioned about the new Measure app (including whether or not it will be a default app), but we can assume it will be available once iOS 12 is released, regardless.