An Equilateral Triangle is one type of triangle where all 3 angles are 60° degrees; and all sides are of equal length.

On this page calculator, you can also calculate the Circumscribed Circle Radius (i.e. the circle drawn that will touch each of its corners/vertices);
and also the Inscribed Circle Radius (the circle drawn that touches the inside edges of the triangle).

Because an equilateral triangle has fixed contraints (fixed angles), the equations can therefore be simplified to the following...
(The height or altitude is the vertical perpendicular height from the base of the triangle)

Area = ¼√3 x Side^{2}

Perimeter = 3 x Side

Height (Altitude) = ⅓√2 x Side

Circumscribed (Outer) Circle Radius = ⅓√3 x Side

Inscribed (Inner) Circle Radius = ⅓√6 x Side

Side

Area

Perimeter

Height

Circumscribed Circle Radius

Inscribed Circle Radius

*All sides, height, radii are in units (e.g. cm), and area will be in unit squares (e.g. cm^{2}).