The volume of mobile phase passing through the column in unit time. The flow rate is usually measured at column outlet, at ambient pressure ($p_{\text{a}}$) and temperature ($T_{\text{a}}$, in $\text{K}$); this value is indicated with the symbol $F$. If a water-containing flowmeter was used for the measurement (e.g. the so-called soap bubble flowmeter) then $F$ must be corrected to dry gas conditions in order to obtain the mobile phase flow rate at ambient temperature ($F_{\text{a}}$): $$F_{\text{a}}=F(1-\frac{p_{\text{w}}}{p_{\text{a}}})$$ where $p_{\text{w}}$ is the partial pressure of water vapour at ambient temperature. In order to specify chromatographic conditions in column chromatography, the flow-rate (mobile phase flow rate at column temperature, $F_{\text{c}}$) must be expressed at $T_{\text{c}}$ (kelvin), the column temperature: $$F_{\text{c}}=F_{\text{a}}\frac{T_{\text{c}}}{T_{\text{a}}}$$