This study sought to develop empirical models to predict soil relative density (ρ rel ) from measurements of horizontal penetrometer resistance (PR) and soil water content (θ g ) in a wide range of soil textures. This permits the comparison of the state of soil compactness in different soil textures. It was hypothesised that model coefficients would be texture-dependent when soil compactness was expressed as bulk density (ρ d ) and that a model with constant coefficients could be obtained when soil compactness was expressed in terms of ρ rel (obtained as the ratio of ρ d to reference bulk density (ρ ref )). Field measurements were conducted in 2014 using a horizontal penetrometer at 0.25 m depth in 10 fields in Switzerland with a wide range of soil textures covering sandy loam, silt loam, loam, clay loam and clay (clay concentration, (CC) = 153-585 g kg -1 and organic matter concentration, (OM) = 9-168 g kg -1 ). At selected locations along the penetrometer measurement transects, cylindrical soil cores were sampled for determination of soil texture, OM, θ g and ρ d . Soil water potential and effective stress (σ') were also estimated for each location. Standard Proctor tests were performed on eight soils with variable textures.Proctor density was well described as a function of CC and OM (R 2 adj = 0.97, RMSE= 0.046 Mg m -3 ) and was used as reference density to obtain ρ rel . From this we developed a model for prediction of ρ rel from PR and σ' that allows comparisons between soils without changes in model coefficients. However, σ' cannot be obtained from on-the-go measurements a nd the model is therefore of limited value for soil compaction mapping. A model for estimating ρ rel from PR and θ g yielded satisfactory predictions (R 2 adj = 0.66, RMSE= 3.3%), although θ g is a texture-dependent measure of soil water that cannot be compared across soils. Moreover, ρ d was well predicted from PR and θ g (R 2 adj = 0.93, RMSE= 0.05 Mg m -3 ), possibly because all our measurements were carried out at similar soil water potential, which implies that θ g carries soil 3 textural information. Future research should test the proposed equations for a wide range of soil water potential values. The findings presented can be of use in developing measurement systems for mapping soil compactness that combine the proposed prediction functions with horizontal penetrometer and water content sensor systems.