The number of square units it takes to exactly fill the interior of a circle.

Try this Drag the orange dots to move and resize the circle. As the size of the circle
changes, the area is recalculated.

A circle is actually a line, one that connects back to itself making a loop. Imagine the circle to be a loop of string. The string itself has no area, but the space inside the loop does. So strictly speaking a circle has no area.

However, when we say "the area of a circle" we really mean the area of the space inside the circle. If you were to cut a circular disk from a sheet of paper, the disk would have an area, and that is what we mean here.

See also Derivation of the circle area formula.

where:

See also Derivation of the circle area formula.

where:

See also Derivation of the circle area formula.

ENTER ANY ONE VALUE | ||

Radius | clear | |

Diameter | clear | |

Area | clear | |

Circumference | clear | |

Use the calculator above to calculate the properties of a circle.

Enter any single value and the other three will be calculated. For example: enter the radius and press 'Calculate'. The area, diameter and circumference will be calculated.

Similarly, if you enter the area, the radius needed to get that area will be calculated, along with the diameter and circumference.

- In the figure above, click on "hide details"
- Drag the orange dot on the edge of the circle to make a random-size circle.
- Now try to estimate the area enclosed by the circle just looking at the squares inside it

- Circle definition
- Radius of a circle
- Diameter of a circle
- Circumference of a circle
- Parts of a circle (diagram)
- Semicircle definition
- Tangent
- Secant
- Chord
- Intersecting chords theorem
- Intersecting secant lengths theorem
- Intersecting secant angles theorem
- Area of a circle
- Concentric circles
- Annulus
- Area of an annulus
- Sector of a circle
- Area of a circle sector
- Segment of a circle
- Area of a circle segment (given central angle)
- Area of a circle segment (given segment height)

- Basic Equation of a Circle (Center at origin)
- General Equation of a Circle (Center anywhere)
- Parametric Equation of a Circle

- Arc
- Arc length
- Arc angle measure
- Adjacent arcs
- Major/minor arcs
- Intercepted Arc
- Sector of a circle
- Radius of an arc or segment, given height/width
- Sagitta - height of an arc or segment

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