Ammonia temperature programmed desorption and the amine decomposition reaction on Brønsted acid sites were used to count acid sites in Faujasite zeolites. Nine zeolites with different Si/Al and six aliphatic and primary amines of dissimilar sizes and chemical characteristics were used. Amine's cations formed on Brønsted acid sites decompose to ammonia and the corresponding alkene at temperatures between 210 °C and 450 °C. The endothermic reaction was followed in a simultaneous thermal analyzer (STA). The technique allows quantifying the number of acid sites accessible to the amines. Varying the amine size makes it possible to compare acid site accessibility in zeolites. Results show that the number of acid sites counted by each amine highly depends on the molecular size and stability of the formed cation. Dicyclohexylamine is big enough not to enter microporous and to count acid sites located in mesoporous and the external surfaces of Faujasite zeolites. It is proposed that the fraction of acid sites measured by a relatively big amine can be used as an acid site accessibility criterion. The procedure can potentially compute only the fraction of acid sites that participate in a particular reaction.