The surface included within a closed figure, measured by the number of square units needed to cover the surface. The area of a plane figure is the extent of the plane figure, measured in units of length squared. The SI unit of area is the square meter (m^{2}), which is the area of a square with sides measuring 1 meter.

The area of a closed plane figure bounded by straight lines can always be determined by subdividing it into triangles and calculating the area of each triangle. The area of any other type of figures can be found either by approximation using the basic geometric shapes or by the process of integration.

The areas of certain common figures are as follows:

Circle (radius r) | r^{2} |

Ellipse (a/b : semimajor/semiminor) | ab |

Parallelogram | (base)(height) |

Rectangle (sides a and b) | ab |

Square (sides a) | a^{2} |

Triangle | (base)(height) |