Experimental tests were carried out in three geometrically similar laboratory-scale wire-plate electrostatic precipitators in order to evaluate the best electric parameter for scaling the equipment. The parameters kept constant were the pseudo-homogeneous electric field, E-p, the current density, j, the dimensionless voltage, U', and the power consumption per unit collection area, P-A. The experimental tests consisted in measuring the overall efficiency of particle removal, which was used as the comparison parameter. The results indicated that, for constant U', efficiency increased with precipitator size. As for the parameters E-p and P-A, the data were scattered and showed no clear tendency. Finally, by keeping j constant, the overall efficiency of the precipitator remained constant ( within +/- 5%), regardless of the precipitator size. Precipitator efficiency increased exponentially with increase in power consumption per unit gas volume, and all data were well fitted to a power law correlation.