Nonagon

The amount of space a regular nonagon takes up is

${\displaystyle A={\frac {9}{4}}a^{2}\cot {\frac {\pi }{9}}=(9/2)ar=9r^{2}\tan(\pi /9)}$

${\displaystyle =(9/2)R^{2}\sin(2\pi /9)\simeq 6.18182\,a^{2}.}$

a is the length of one of its sides.