How to measure your lawn for a robot mower
Area
Trace the mowable area in a free maps app to get square feet. 1 acre = 43,560 sq ft.
Slope
A smartphone level app gives degrees; percent slope = tan(angle) × 100 (22° ≈ 40%).
Clutter
Count trees, beds and narrow passages. Product pages list the number of zones and no-go areas; more clutter means you want more of both.
Practical guidance; check each maker's requirements (some navigation needs a clear view of the sky).