What instrument measures area?

Answer 1

An instrument that measures area is called a planimeter. A planimeter is a mechanical device used to calculate the area of a two-dimensional shape by tracing its outline. It works by integrating the distance traced by a point on the planimeter's arm as it moves around the shape, providing an accurate measurement of the enclosed area.

Answer 2

your Brain

AnswerOne instrument for measuring areas is a Planimeter.
Area is not normally measured directly: it is usually derived from measurements of lengths. Tools that may be used for that are micrometer, vernier callipers, ruler, measure tape, range-finder, odometer etc.
you can use a meter ruler or a measuring tape. but then, it depends on which measurements do you want to use. some people use centimeter, some use meter, some kilometer.
Well, if you want to know the name of an instrument wich is able to measure an area:

planimeter

http://en.wikipedia.org/wiki/Planimeter