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`A = pi*r^2`

Enter a value for all fields

The **Area of a Circle** equation (A = π•r²)* CIRCLE PARTS * computes the area of a circle.

**INSTRUCTIONS:** Choose units and enter the following:

- (
**r**) - Radius of the circle

**Area of a Circle (A):** The calculator computes the area (**A**) in square meters. However, this can be automatically converted to many other area units (e.g. square inches) via the pull-down menu.

- Light and Matter(Dr. Benjamin Crowell) Chapter 0.5 Basics of the Metric System
- Light and Matter(Dr. Benjamin Crowell) Chapter 1.1 Introduction

**Related Calculators:**

**Circle Area**- This computes the area of a circle given the radius**(A = π r**.^{2})**Segment Area f(r,θ)**- This computes the area of an arc segment of a circle given the radius (**r**) and angle (**θ**)**Segment Area f(r,h)**- This computes the area of an arc segment of a circle given radius (**r**) and the depth (**h**) into the circle.**Sector Area f(r,Θ)**- This computes the area of a sector (pie slice) of a circle given the radius (**r**) and angle (**Θ**).**Area of Annulus**- This computes the area of an annulus (ring) given the inner radius (**r**) and outer radius (**R**).**Radius -Center to a Point**- This computes the radius of a circle given the center point (**h,k**) and any other point (**x,y**) on the circle.**Circumference**- This computes the circumference of a circle given the radius (**C = 2 π r**).**Arc Lengths**- This computes the length of a cord segment (arc length) on a circle given the radius (r) and angle (**Θ**)**Circle within a Triangle**- This computes the radius of a circle inscribed within a triangle given the length of the three sides (**a,b,c**) of the triangle.**Circle around a Triangle**- This computes the radius of a circle that circumscribes a triangle given the length of the three sides (**a,b,c**) of the triangle.**Radius from Circumference**- This computes the radius of a circle given the circumference.**Circumference from Area**- This computes the circumference of a circle given the area.**Radius from Area**- This computes the radius of a circle given the area.**Radius from Chord**- This computes the radius of a circle based on the length of a chord and the chord's center height.

The formula for the area of a circle is:

A = π•r²

where:

- A is the area of the circle
- r is the radius of the circle

A **circle** is a simple shape in Euclidean geometry. It is the set of all points in a plane that are at a given distance from a given point, the center; equivalently it is the curve traced out by a point that moves so that its distance from a given point is constant. The distance between any of the points and the center is called the radius.

A circle is a simple closed curve which divides the plane into two regions: an interior and an exterior. In everyday use, the term "circle" may be used interchangeably to refer to either the boundary of the figure, or to the whole figure including its interior; in strict technical usage, the circle is the former and the latter is called a disk.

A circle may also be defined as a special ellipse in which the two foci are coincident and the eccentricity is 0, or the two-dimensional shape enclosing the most area per unit perimeter, using calculus of variations.

- Area of Circle - Circle approximates a polygon as the number of sides approaches infinity.
- Area of Triangle - Three Sides
- Area of Quadrilateral - Four Sides
- Area of Pentagon - Five Sides
- Area of Hexagon - Six Sides
- Area of Heptagon - Seven Sides
- Area of Octagon - Eight Sides
- Area of Nonogon - Nine Sides
- Area of Decagon - Ten Sides
- Area of Hendecagon - Eleven Sides
- Area of Dodecagon - Twelve Sides
- Area of Polygon - Any number of sides (n).