Area of a Parallelogram
Today we are going to calculate the area of a parallelogram. But, of course, we must first define what a parallelogram is.
What is a parallelogram?
A parallelogram by definition has four sides. In the picture shown, the sides are labelled just a and b because the opposite sides of a parallelogram must be of the same length. However, unlike a rectangle, the sides do not have to be perpendicular to one another. In another word, a rectangle is a parallelogram with perpendicular sides.
So, if you have a geometrical shape with both opposite sides parallel to each other, then you have a paralellogram.
Now, with each parallelogram, there is a perpendicular height between the two parallel sides. The perpendicular height from the base b of the parallelogram is labelled 'h'. The formula for calculating the area of a parallelogram is simply this.
Formula for area of parallelogram
In another word, the area of a parallelogram is its base times its perpendicular distance to the opposite parallel side. Now, whether you measure h from b or from a, the resulting area of the parallelogram will be the same.

In another word, a x h_{1} = b x h. 
