I Need To Know The Formula To Calculate The Area Of A Cylinder?

Area of the cylinder = base area x height.

Since a cylinder has a circular base, the base area = ∏r²

Therefore:
A = ∏r²h (where A is the area, h is the height and, r is the base radius and ∏ = 22/7)

If you really mean the AREA of a cylinder, you must mean the Surface Area. For that, imagine cutting the cylinder (a can) downward and flattening it out. The surface area of the cylinder is area of the rectangle formed, whose height is the same as the height of the can, and whose length is the circumference of the can's top, or 2 x Pi x Radius.If you mean the VOLUME of a cylinder (a can), it's Pi x R squared x H.

V=pie x radius(squared) x height

I need to know to calculate the cross sectional area of cylinder.

Volume of cylinder