The thermal conductivity of the soil skeleton λs is an essential parameter from the point of view of the correct assessment of soil overall/effective conductivity. This work introduces the concept of “local thermal conductivity fluctuation” which characterizes the microscale variation of conductivity within the solid phase. It is proposed to link the “local fluctuation” of thermal conductivity λ with the soil texture – the information that is available at the scale of engineering applications. It was possible to relate the skeleton thermal conductivity with the grain size distribution of the soil. Finally, based on a large series of numerical simulations, the paper provides four triangle diagrams (at different organic matter contents: 0%, 2%, 4% and 6%) relating the value of λs with volume fraction of individual soil separates. This result is extremely important from the practical point of view. One can quickly evaluate λs value provided that information on the grain size distribution and organic matter content is available.