Method for the measurement of the hardness and for the selection of agricultural products, comprising the following operations: - implementing a test program suitable of identifying and of selecting one or more indexes (S3, S4) correlated to the hardness (Du) of said agricultural product measured by a respective penetration test, said test program using measurement data of a penetrometer hardness test (Du) on a first agricultural product and a non-destructive test comprising measurement data detected by at least a piezo-electric transducer (24, 35) of at least the crossing time (Δt) and the length of the path (Δl) of a dynamic force applied to and crossing through said first agricultural product and measurement data of the weight (m) of the first agricultural product, - calculating the equation coefficients (a, b) defining the linear correlation Du=b*Sn+a between said one or more indexes (S3, S4) and the respective hardness (Du) of said first agricultural product, where Sn indicates said one or more indexes (S3, S4), wherein a first identified index of said one or more indexes (S3, S4) is defined by the relationship S4 = m / (Δl * Δt 2), where Δl is the length of the path of a dynamic force crossing said first agricultural product, Δt is the crossing time of said dynamic force through said first agricultural product and m is the weight of said first agricultural product, wherein said hardness (Du) of a second agricultural product correlated to said first index is measured according to the following operations: - measuring the weight (m) of said second agricultural product, - applying to said second agricultural product a dynamic force through a first piezo-electric transducer able of generating a first electric signal referred to the application of said dynamic force, - detecting the dynamic reaction of said second agricultural product through a second piezo-electric transducer able of generating a second electric signal referred to the transmission of said dynamic force through said agricultural product, - analyzing said first and second electric signals correlated to the hardness of said second agricultural product, and measuring said crossing time (Δt) and said path length (Δl) of said dynamic force across said second agricultural product, - calculating said first index as S4 = m / (Δl * Δt 2), - determining the hardness (Du) of said second agricultural product by comparing the measured first index to said linear correlation Du=b * S4+a. - implementing a test program suitable of identifying and of selecting one or more indexes (S3, S4) correlated to the hardness (Du) of said agricultural product measured by a respective penetration test, said test program using measurement data of a penetrometer hardness test (Du) on a first agricultural product and a non-destructive test comprising measurement data detected by at least a piezo-electric transducer (24, 35) of at least the crossing time (Δt) and the length of the path (Δl) of a dynamic force applied to and crossing through said first agricultural product and measurement data of the weight (m) of the first agricultural product, - calculating the equation coefficients (a, b) defining the linear correlation Du=b*Sn+a between said one or more indexes (S3, S4) and the respective hardness (Du) of said first agricultural product, where Sn indicates said one or more indexes (S3, S4), wherein a first identified index of said one or more indexes (S3, S4) is defined by the relationship S4 = m / (Δl * Δt 2), where Δl is the length of the path of a dynamic force crossing said first agricultural product, Δt is the crossing time of said dynamic force through said first agricultural product and m is the weight of said first agricultural product, - measuring the weight (m) of said second agricultural product, - applying to said second agricultural product a dynamic force through a first piezo-electric transducer able of generating a first electric signal referred to the application of said dynamic force, - detecting the dynamic reaction of said second agricultural product through a second piezo-electric transducer able of generating a second electric signal referred to the transmission of said dynamic force through said agricultural product, - analyzing said first and second electric signals correlated to the hardness of said second agricultural product, and measuring said crossing time (Δt) and said path length (Δl) of said dynamic force across said second agricultural product, - calculating said first index as S4 = m / (Δl * Δt 2), - determining the hardness (Du) of said second agricultural product by comparing the measured first index to said linear correlation Du=b * S4+a.