取 $A(0,0,0)$ 為參考點： $$\overset{\large\rightharpoonup}{AC}=(1,1,0),\ \overset{\large\rightharpoonup}{AF}=(1,0,1),\ \overset{\large\rightharpoonup}{AH}=(0,1,1)$$ 體積： $$V = \dfrac{1}{6}\left|\det(\overset{\large\rightharpoonup}{AC},\overset{\large\rightharpoonup}{AF},\overset{\large\rightharpoonup}{AH})\right|$$ $$\det = \begin{vmatrix}1 & 1 & 0\\ 1 & 0 & 1\\ 0 & 1 & 1\end{vmatrix} = 1(0-1)-1(1-0)+0 = -2$$ $$V = \dfrac{|-2|}{6} = \dfrac{1}{3}$$