Hendecagon

The amount of space a regular hendecagon takes up is

${\displaystyle \alpha ={\frac {(n-2)}{n}}\cdot 180^{\circ }={\frac {9}{11}}\cdot 180^{\circ }\approx 147{,}273^{\circ }}$

${\displaystyle A={\frac {11}{4}}a^{2}\cot {\frac {\pi }{11}}\approx 9,36564a^{2}\,}$

a is the length of one of its sides.