Online area calculator tool for Google maps. In the example below, the area of Puerto Rico is calculated to be 8,939 km^2. The official area is closer to 9,100 km^2. I created the map below quickly (in about 1-minute), but I could probably obtain a more accurate estimate of area if I took a bit more time. This tool could be valuable for estimating the area of farm fields, catchment areas for estimating surface runoff, etc.