TAPPI T 509 om-15 measures the hydrogen ion concentration of a cold aqueous extract (unfiltered) of paper, expressed in terms of pH value.

It is suitable for writing, printing, and sized industrial papers, but is not intended for unbuffered types such as insulating and condenser papers. The determined values may not be exact in a fundamental sense and should not be interpreted in terms of solution theory. The pH values are empirically correlated with end use requirements and paper qualities. This method avoids change of acidity or alkalinity resulting from heat-induced hydrolysis.

A hot water extraction method is described in TAPPI T 435, Hydrogen Ion Concentration (pH) of Paper Extracts (Hot Extraction Method).

Surface pH measurement of paper is described in TAPPI T 529, Surface pH Measurement of Paper.