Segi delapan

Luas

${\displaystyle L=2\cot {\frac {\pi }{8}}a^{2}=2(1+{\sqrt {2}})a^{2}\simeq 4.828\,a^{2}.}$

Diagonal

${\displaystyle d_{1}=2\cdot r_{\mathrm {r} }={\sqrt {4+2{\sqrt {2}}}}\cdot a\approx 2{,}613\cdot a}$

${\displaystyle d_{2}=2\cdot r_{\mathrm {l} }=(1+{\sqrt {2}})\cdot a\approx 2{,}414\cdot a}$

Jari jari lingkaran

${\displaystyle r_{\mathrm {l} }={\frac {1+{\sqrt {2}}}{2}}\cdot a\approx 1{,}207\cdot a}$

Radius

${\displaystyle r_{\mathrm {r} }={\frac {1}{2}}\cdot {\sqrt {4+2{\sqrt {2}}}}\cdot a\approx 1{,}307\cdot a}$

Sudut tengah

${\displaystyle \alpha ={\frac {360^{\circ }}{8}}=45^{\circ }}$

Sudut interior

${\displaystyle \delta =180^{\circ }-\alpha =135^{\circ }}$