Soil depth refers to the depth of unconsolidated soil layers and is restricted in vertical extent by the occurrence of solid rock, solidified or hardened layers, or a predominant coarse fraction. The Agricultural Soil Map of Austria distinguishes a total of six classes, three primary and three secondary classes. The primary classes comprise "shallow" (<30cm), "medium" (30cm - 70cm), and "deep" (>70cm), while the secondary classes include the transition classes "shallow to medium," "medium to deep," and "highly variable." Soil depth as distinguished in this map refers to the extent to which a manually-operated soil drill (“Pürckhauer”) can be driven into the soil. This should not be confused with the soil depth to which root growth is possible known as the "effective depth" or "physiological depth". Typically, physiological depth extends beyond soil depth, since plant roots can partially penetrate dense layers or layers with a high proportion of coarse material.

Nevertheless, the soil depth offers a suitable estimate of the soil volume accessible for root growth, as well as the soil's capacity to retain water and nutrients.