No, you need to include the height of the cylinder (a). Imagine a deep dish pizza (big a) versus a thin crust (small a) - the sides of the deep dish pizza have more area. Your formula returns the circumference of the pizza.

If you’re interested in dimensional analysis (and why wouldn’t you be?) the formula you proposed doesn’t have enough length units. It would return a value of length (like inches, or cm) not area (like square inches or square cm).