Identification of similar soils is an important step in different branches of soil hydrology. Generally, a characteristic length in porous media is used for estimating scaling factors in a similarity analysis. Such an approach amounts to the use of the first moment of the pore size distribution (PSD). Previous research has suggested that the σ of PSD of similar soils should also be similar. Authors of this research proposed a new criterion in terms of the CV for σ (CVσ) with the suggestion that the “geometrically similar” soils should satisfy the condition of CVσ < 10%. Here, we validate this result using the aggregate size distribution (ASD) data of 1375 soils collected from 10 different zones with varying scale and properties. The lognormal distribution function and the physically based scaling (PBS) approach were used to scale the ASD datasets. The effectiveness of scaling was determined by the RMSE between the scaled ASD curve and the reference ASD curve. Four out of 10 soil datasets had CVσ < 12%, and their corresponding RMSE values were an order of magnitude lower than those for the remaining soil groups. A plot between the RMSE and CVσ values showed that CVσ < 10% may be used as a practical limit for identifying similar soils.

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