Thermoelectric materials are substances that produce electric potential when some temperature difference is applied to them, or by applying an electric potential difference we observe a temperature gradient in the material. Today, these materials have many applications, including water heaters, water coolers, solar cells, and thermal sensors. For this reason, researchers are looking for materials that have better thermoelectric properties. In the meantime, topological insulators have been considered for their unusual thermoelectric properties. These materials are insulating in the interior and conductive on their surfaces. This causes the conductive surface states to overcome the insulating bulk states and allows the material to exhibit better thermoelectric properties. Now, there is sufficient motivation for research in this subject. In this thesis, we calculated the thermoelectric efficiency of topological insulators. Thermoelectric efficiency is introduced for ordinary materials. Then, due to the different role played by the bulk and surface states in a topological insulator, thermoelectric efficiency was calculated for each section separately. In the following, using the MATLAB programming language and the results of the relationship between the thermoelectric efficiency of a topological insulator and the thickness of that material, was analyzed. It is shown that the thermoelectricity in topological insulators is dependent on the size of the material, which is different from ordinary thermoelectric materials.