SizeMatters is a simple AR (augmented reality) app that allows you to measure anything through your phone. This was published to the app store before Apple announced iOS 12 (which included their own AR measuring app).
Users can switch their measurment unit between centimeters, inches, feet and meters.
Clicking on the round button will take a screenshot of the measurment and save it to the iPhones photo library.
Feel free to download the app and play around with it. https://itunes.apple.com/us/app/sizematters/id1398483145