Measure from one vertex to another directly across from it. There are three possible lines to take this measurement on.
Divide the measurement from Step 1 by two to yield the radius. For example, if the measurement was 6 cm, the radius of the hexagon is 3 cm.
Multiply the radius by six to yield the perimeter of the hexagon. In this example, the perimeter is equal to 6*r, or 18 cm.
Take the square of the radius and multiply that value by (3*sqrt(3))/2 to yield the area. In this example, the area is ((3*sqrt(3))/2) *(3^2), or 23.4 cm^2.