Area of a Circle Calculator [raw] Radius(r) millimeters(mm) centimeters(cm) ... formulas manually to find the area, circumference, radius and diameter of a circle, this ... the circumference is c = π(8) = 8π or 25.1 cm, rounded to the nearest tenth. ... a = π(25) = 25π. If rounding to the nearest tenth the area is 78.5 square inches.
