The aim of proposed thesis is to develop a model for direct determination of standard assemblies effective area over basic SI units: mass and length. Proposed model has been confirmed experimentally through comparison with other primary pressure standards. The methodology of conducted research is based on combination of science and engineering methods, by synthesis of theoretical methods and practical experiments. Fundamentals of physical models used for characterization of piston gauges and dive-bell manometers are given. Based on the study of standard piston/cylinder assemblies three models for the effective area determination have been developed. Proposed models (ideal, conical and real) are based on Dadson's theory. Description of experimental methods for effective area determination based on comparisons with other pressure standards is included. Overview of measurement uncertainties are given including the methods of uncertainty determination as an integral part of every measurement. Methods and capabilities of leading international measurement institutions are described as well as description of pressure traceability in Croatia. Experimental part of research has been conducted in LPM and partially in German national laboratory for pressure at Physikalisch Technische Bundesanstalt (PTB) in Braunschweig. Partially measurements have been also conducted in the national laboratories for mass and length. Four standard measurement facilities, with internal identity marks: M832, X0013, X0046 and TLVAG-05, covering the pressure interval from 0 up to 140 MPa have been described. The work points out comparison of two independent methods for effective area determination every standard assembly which is also the most influential component in the estimation of pressure measurement uncertainty. Mathematical models for effective area determination based on dimensional measurements are developed as well as for the estimation of the measurement uncertainty. Experimental method for the estimation of Piston/cylinder effective area measurement is described comparatively with the standard assemblies of German PTB institute. Measurement results of and calculation of influence quantities are given with the measurement uncertainties for all four measurement assemblies. Differences in effective areas compared to PTB measurement results have been statistically analyzed by estimation of normalized deviation factor En. It has been shown that measurement uncertainties in calibration of pressure standard are in the range U=(5•10-5•pe)Pa; (k=2). Therefore a double characterization of primary pressure standard has been established: over the basic SI units and by direct comparisons with other primary pressure standard.