Quality factors associated with formation pressure measurements at various depths in the geologic formation are determined based on one or more well logs of formation properties in a geologic formation. A formation testing tool with two or more probes is positioned in a borehole of the geologic formation based on the quality factors. The two or more probes in the borehole perform respective formation pressure measurements, where each formation pressure measurement is performed at a different depth. The formation pressure measurements and the given distance between the two or more probes indicate a formation pressure gradient.