Area of a Circle Calculator

The area of a circle measures the two-dimensional space enclosed by its curved boundary. It is found with the formula A = pi × r², where r is the radius and pi is the constant approximately equal to 3.14159265. Squaring the radius is essential because area describes a surface rather than a length. If a circle has a radius of 5 centimeters, its area is pi × 25, or about 78.54 square centimeters. The unit is always squared, so a radius measured in meters produces an area in square meters. This calculator also finds circumference and diameter because all three circle measurements are connected by the radius. Diameter is twice the radius, written d = 2r. Circumference is the distance around the boundary and is calculated with C = 2 × pi × r. Keeping these values together is useful in geometry exercises, construction layouts, machining, landscape design, packaging, and any task involving round objects. Enter the radius once and the calculator applies each canonical formula without requiring separate conversions. A radius runs from the center of a circle to any point on its edge. A diameter crosses the whole circle through its center, so it contains two radii. Be careful not to enter a diameter as though it were a radius: doing so makes the calculated diameter twice too large and the area four times too large. If you know only the diameter, divide it by two before using the calculator. If you know circumference, divide it by two times pi to recover the radius. The selected unit does not alter the numerical formula; it labels the dimensions correctly. For example, a radius of 10 inches gives a circumference of about 62.83 inches and an area of about 314.16 square inches. Convert the radius before calculating if you need results in a different measurement system. One inch equals 2.54 centimeters, while one foot equals 12 inches. Because area scales with the square of length, an area conversion uses the square of the linear conversion factor. Results are shown to practical decimal precision using the full pi constant supplied by JavaScript rather than the rough value 3.14. This gives accurate answers for school mathematics and everyday planning. For manufacturing or regulated engineering, preserve enough significant figures for the tolerance of the original radius measurement. A more precise calculator cannot compensate for an imprecise input, so record the radius carefully and round only the final answer.