The number of CubeSats launched to space has largely increased during last years. Any kind of satellite, even CubeSats, need to have some control on their attitude for pointing, i.e. antenna to Earth or solar panels to Sun. Among the available technology to control the attitude, CubeSats usually have cylindrical coils called magnetorquers, whose magnetic field interacts with the Earth’s magnetic field. CubeSat To verify its performance, it can be used a testing facility capable of simulating magnetic field along the satellite orbit. This work presents a metrological uncertainty analysis of a testing facility based on Helmholtz cage. Magnetic field uncertainty is obtained by performing uniformity, stability and gaussmeter calibration error tests. To simulate low Earth orbit satellite magnetic field conditions, the International Geomagnetic Reference Field model is used. The operation algorithms and software, developed using Python language, are validated by contrasting its results with Systems Tool Kit software, a commercial package, showing a maximum relative error of 0.03 %. Values from the testing facility are compared with in-situ measurements from Lume-1 satellite on-board gaussmeter, showing a maximum discordance lower than 50 mG. Keywords: spacecraft tests; attitude control system; Helmholtz facility; uncertainty evaluation; metrology