The pH measurement in chemical analysis is an important index in numerous applications, e.g. chemical engineering, environmental science, materials science, biochemistry, pharmaceutical industry. Routine pH measurements are carried out with pH meter-glass electrode assemblies. The use of these electrodes is subject to various effects, producing uncertainties of unknown magnitude. Therefore, the measurement of pH requires a suitable calibration by certified standard buffer solutions traceable to primary pH standards. This monograph addresses the optimal experimental procedure for the calibration problem to common pH meters, under D- and c-optimality criteria. By considering the simple regression model, the main target is to estimate as a nonlinear function the calibrating value. Two optimal design procedures are adopted to tackle the problem: D- and c-optimality. Therefore various data sets are examined, under the D- and c-optimal approach, to obtain the appropriate model for calibrating pH meters.