In geometry, perimeter is the distance around a flat object. For example, all four sides of a square rhombus have the same length, so a rhombus with side length 2 inches would have a perimeter of 8 inches (2+2+2+2=8).

For a polygon, the perimeter is simply the sum of the length of all of its sides. For a rectangle, the perimeter is twice the sum of its length and width (\displaystyle{ P=2 \ell + 2w }). Perimeter can also be calculated for other planar figures, such as circle, sector and ellipse.