Enter a side length or perimeter to calculate a regular pentagon's area and apothem.
How to Use the Pentagon Calculator
Choose Side or Perimeter, enter the value, and the pentagon's area, apothem, and circumradius fill in below.
perimeter = 5 × side
apothem = side ÷ (2 × tan(36°))
area = ¼ × √(5(5 + 2√5)) × side²Home plate, the Pentagon building, and a lot of garden-bed layouts use a regular pentagon's five equal 108° angles — an odd number of sides that, unlike a square or hexagon, can't be split into a whole number of identical rectangles or equilateral triangles, which is exactly why its area formula is the least tidy-looking of the small regular polygons.