Indonesia has quite large potential and reserves of non-metallic minerals, which are spread almost evenly throughout the region. Excavated materials include andesite, amounting to 18.98 billion tons, one of which is in the province of East Java. Estimating subsurface andesite reserves is urgent, as a first step in exploration. The presence of andesite below the surface is searched using Geophysical methods, one of which is Geoelectric. Processing geoelectric data using inversion produces inversion modeling, which is used to interpret geoelectric data. This research compares Least Square and Robust Inversion data to estimate andesite resources in the Tugu Area, Trenggalek Regency. The research results show that the Least Square inversion results have a smaller error than the Robust, but the cross-section of the Robust inversion is smoother than the Least Square inversion results. The Robust inversion cross-section has a higher resistivity value than the Least Square Inversion cross-section. Based on the resistivity range of the two inversion results, the areas are divided into three lithologies. Low resistivity values < 200 Ωm are soil, medium values (200–500) Ωm are indicated as weathered andesite, and high values > 500 Ωm are indicated as compact andesite.