In Thermogravimetry (TG) and TG/FTIR systems, there are many variables that can affect the detection limit of the system. It is demonstrated in this paper that the larger the sample size, the better the detection limit. For TG/FTIR, with a certain kind of TG/FTIR interface, the detection limit is dependent upon the sample holder volume of the TG system. It is proved that, for a sample mixture, the ratio of balance sensitivity to standard sample holder volume should be used to characterize the detection limit of TG, while the standard sample holder volume of the TG system should be used to characterize that of TG/FTIR.