Thanks brynn for the quick answer.
I think I will do it this way, using the measurement extension.
Just another question: why when i'm using the Path>>Division sometimes it doesn't work (i draw a line over the polygon, select both and when I choose division everything disappear)?

Hello, I'm new to Inkscape and I'm trying for a while to perform a task without success. Does anyone know how could I split a irregular polygon based on it's area? For example, let's say i have a polygon representing a country and I want to split it in two parts, one with 60% of the area and the oth...