AbstractLimestone dissolution occurs as a surface reaction; therefore, the particle‐size distribution of the material influences its reactivity. Particle‐size distribution alone, however, may not provide a good comparative index of reactivity because of differences in mineralogy, surface composition, and morphology. A pH‐stat titration procedure was previously developed to determine the “effective” reactivity of soil carbonate. The objective of this study was to evaluate the pH‐stat procedure as a method for comparing the reactivities of liming materials. Eighteen liming materials, representing a wide range of physical and chemical properties, were analyzed. The relative reactivities of the materials are expressed as Iceland‐spar reactivity equivalent (ISRE), and reported as particle‐size distribution (ISRE‐PSD) or surface area (ISRE‐SA) of a standard Iceland‐spar calcite that has the equivalent quantity and reactivity as the sample. The ISRE‐PSD of the calcitic materials gave higher proportions of fine‐clay‐size particles than were obtained by sieving and sedimentation, indicating that the calcitic liming materials had greater surface reactivities than the Iceland‐spar calcite standard. The dolomitic materials, being less reactive than the calcitic materials, exhibited large proportions of ISRE fine‐sand‐size particles and small proportions of ISRE clay‐size particles. Calculations of surface area using ISRE‐PSD data provide a more explicit index of reactivity than the ISRE‐PSD. The ISRE‐SA values of the calcitic and dolomitic materials were not highly correlated with surface areas determined by the Brunauer‐Emmett‐Teller (BET) or sedimentation procedures, indicating the pH‐stat procedure provides a method for comparing the reactivities of liming materials not possible by BET, sieving, or sedimentation methods.