In leaf gas exchange measurements, cuticular conductance to water (g_cw) is indistinguishable from and included in stomatal conductance to water vapor (g_sw). Here we developed a simple technique to isolate g_cw by directly measuring leaf intercellular CO₂ concentration (C_i(m)) along with gas exchange during photosynthetic light induction. We derived stomatal conductance to CO₂ (g_sc(m)) from the C_i(m) independently of g_sw. Plotting g_sw against g_sc(m) during the early induction phase within ~10 min, we found a highly linear relationship with a positive intercept. Assuming negligible cuticular CO₂ transport, complete stomatal closure occurs when g_sc(m)=0. Then, we considered the residual g_sw (i.e., intercept) as g_cw. Indeed, these g_cw estimates succeeded in correcting the calculation. Our technique, owing to its robustness and increased throughput, will allow for more rapid screening of crops, more reliable gas exchange analysis, and more accurate prediction of plant function under natural environmental conditions.