Hexagonal unit-cell volume ($V_{\mathrm{cell}}=\sqrt{3}{a}^{2}c/2$)

For basal vectors of equal length $a$ separated by120degrees and perpendicular height $c$, cell volume is $a^{2}c\sin 120^{\circ }=\sqrt{3}{a}^{2}c/2$. A full hexagonal prism drawn around it has three times this volume and must contain three times as many atoms if used for density calculations.