Conventional ammeters should be inserted in series with the element in which the current is to be measured, thus constituting an invasive measurement form. Clamp ammeters, based on coils, are able to measure non-invasively but are limited to alternating currents. For measurement of direct currents, Hall-based ammeters are used, but have low output voltages and little temperature stability. Thus, the objective of this dissertation was to develop a prototype based on giant magnetoresistance (GMR) magnetometers capable of measuring direct currents, non-invasively and with high resolution in relation to clamp ammeters. The methodology was divided into: (i) the use of two GMR magnetometers to measure the magnetic field generated by the electric current in a conductor; (ii) design and implementation of a solenoid to polarize the sensors in the linear operating range; (iii) improvement and development of electronic circuits dedicated to the excitation and reading the GMRs; (iv) implementation of algorithms to solve the inverse problem, that is, from the outputs of the circuit, in mV, estimate the current passing through the conductor and the distance between it and the ammeter. Sixty tests were performed, with currents varying from -3 A to 3 A, with steps of 0.1 A. The prototype was able to estimate the electrical current with type A expanded uncertainty of 0.091 A and 0.07 cm for the distance. The results demonstrate the feasibility of conducting current measurements by approximation using GMR sensors.