Calculate floor surface area (square feet/metres) - how? TONIGHT!

[tim_in_oz]

Hi guys,
is there an easy way to calculate floor surface area of a room or several rooms?

If not a plug-in, is there an easy way people recommend?

Right now I'm thinking of resorting to creating extra large furniture that fits the space and adding up the measures of that.

Want to do this asap, ideally tonight!

[Puybaret]

This is not really a feature, but if you create a room by double-clicking on a wall (instead of inside an area surrounded by walls), this will create a room that will cover all the walls touching each other and their inner areas.