Outer radius r_o
Outer radius r_o
Number of sides 12
Side length a_12=r_o*2*sqrt((5-sqrt(5))/2)
Area A=3*a*a/tan(pi/12)
sum of sides 12*a_12
Outer angle 360/12
Radius of inner circle r_i=a/(2*tan(36))
Diagonal d=2* r_o
Height h = 2 \cdot r_i
Sum of angles 1800


Description at Wikipedia

deesDodecagon (12 sides)
Geometry 2D Mathematics Online calculators