The application of phenol red has been widely applied in cell culture media to enable monitoring of the pH value of cell growth. However, sometimes it is difficult for a human observer to identify the colour transformation using only the naked eye. Furthermore, different people will give different interpretations of colour transformation. Thus the current study was performed to provide the spectrophotometry and colorimetry profiling of pure phenol red and cell culture media to pH variation. Pure phenol red and cell culture media were used as samples. The pH values of both types of sample were manipulated using citric acid. Spectrophotometry analysis results show that the pH value of the pure phenol red samples could be well profiled by using the wavelengths in the green light region (in the range of 500‐600 nm). The pH value of the cell culture medium samples could also be well profiled, by using wavelengths in either the green or blue light region. Colorimetry analysis results conducted using CIELab colour space indicate that the colour transformation of both samples is linear, with a high value for the coefficient of determination. This profiling proves that phenol red can be used to quantify the pH values of the samples and shows good potential to be applied in the development of spectroscopy‐based and colorimetry‐based pH sensors.