The geometric volume of the part of the tube that contains the packing: $$V_{\text{c}}=A_{\text{c}}L$$ where $A_{\text{c}}$ is the internal cross-sectional area of the tube and $L$ the length of the packed part of the column. In the case of wall-coated open-tubular columns the column volume corresponds to the geometric volume of the whole tube having a liquid or a solid stationary phase on its wall.