volume of parallelopiped given four vertices

Assume we are given four vertices $A$ to $D$. Treat the $A$ as the origin and calculate three vectors $\vec{P}=\overrightarrow{AB}$, $\vec{Q}=\overrightarrow{AC}$, and $\vec{R}=\overrightarrow{AD}$. These three vectors are the three edges ending on the same vertex. The volume is the triple scalar product of $\vec{P}$, $\vec{Q}$, and $\vec{R}$, i.e., $\vec{P}\cdot (\vec{Q}\times \vec{R})$, or find the determinant of their matrix from vertical concatenation).