This app was mentioned in 3 comments, with an average of 1.67 upvotes
Called a planimeter app. Here's one, but there are also some free apps out there I think.
We have recently published update to <strong>Planimeter- GPS Area Measure</strong> app with ability to bookmark (make notes) locations for mapping purposes. You can save your pins, open and edit notes and quickly switch to Google Maps navigation for the selected point. Please see the demo video below: