The integrated molar absorption coefficients of the infrared bands characteristic of adsorbed lutidine (2,6-dimethylpyridine) were determined for the purpose of quantifying the acid sites of solid catalysts. The integrated molar absorption coefficients were measured for lutidine adsorbed through H-bonding, coordination to Lewis sites and protonation on Brønsted acid sites. The solids were chosen to present all possible bondings with lutidine and to cover a wide range of common types of catalysts or supports: silica, phosphated silica, HY zeolite, alumina, zirconia, WOx supported on zirconia and NbOx supported on zirconia.