This paper presents the methodology for calculating the peak deviator stress and strain uncertainty of triaxial compression tests on water saturated, non-cohesive soils consolidated under isotropic conditions, following the ISO 17892-9:2018 [1] standard test method. A silicious sand sample of known properties is compacted with the same water content targeting the same bulk density to produce identical cylindrical specimens. These are then tested under the same conditions. Type A and type B uncertainties are both calculated based on BIPM et al. [2]. Type A is calculated from the tests performed under the same conditions. Type B is obtained by applying the propagation method and incorporating the uncertainty of each individual measuring device used during the test. The combined and expanded uncertainty can then be calculated from the type A and type B uncertainties. The conditions of the experiment, including the assumptions made and the variables that are kept constant, are described. The paper concludes with an assessment of the results obtained.