Calculate the area and circumference of a circle. Enter the diameter or radius to size round patios, tabletops, rugs, or gardens.
Circle Area
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Area in square units.Usage Tip
Measure the diameter across the widest point through the center and divide by two for the radius — it is easier and more accurate than guessing the center.
THE MATH
Area = π × radius²
Circumference = π × diameter
Radius = diameter ÷ 2
Circumference = π × diameter
Radius = diameter ÷ 2
Enter the diameter (full width across the center) or the radius (center to edge). Area is in square units; circumference is the distance around.
π (pi) is about 3.14159.
π (pi) is about 3.14159.
For a round patio, tabletop, or rug, the area sizes the material and the circumference sizes any edge banding or trim.
For a ring or donut shape, find the outer and inner circle areas and subtract.
Round materials are often sold as squares or by the linear foot of a roll — add waste for the corners you cut off.
For a ring or donut shape, find the outer and inner circle areas and subtract.
Round materials are often sold as squares or by the linear foot of a roll — add waste for the corners you cut off.