We present the structure of an electrode and the excitation frequency that reduces the estimation error when the concentration of a reagent is measured using impedance. To compare the performance characteristics of interdigitated electrodes with one to five fingers, five electrodes of the same type were fabricated independently on printed circuit board (PCB) substrates. A fluidic channel was created on each substrate using double-sided tape and a polycarbonate (PC) cover so that the solution was equally distributed over all electrodes. The impedance was measured with stimulation signals of various frequencies for various concentrations. The measured impedance was used to calculate a linear parameter between the concentration and the impedance, and this parameter was used to calculate the error between the estimated value obtained from the impedance and the original concentration. Using this estimation error as a measure, we investigated the electrode and stimulus frequency suitable for each application requiring either lot or individual calibration. Experimental results show that measuring impedance at high frequencies with a single-finger electrode is advantageous for applications requiring lot calibration, while multiple-finger electrodes are suitable for individual calibration applications at low frequencies.