Aeolian processes on Mars form a distinct class of meter-scale ripples, whose mechanisms of formation are debated. We present a global morphometric survey of bedforms on Mars, adding relevant observational constraints to the ongoing debate. We show that the bedforms located in the Tharsis region form a distinct group, not akin to the large dark-toned ripples which cover dune fields elsewhere on the planet. The relation between wavelength and atmospheric density derived from the new data is consistent with the predictions of a wind-drag mechanism, favoring the model that uses a saltation saturation length. Regardless of the mechanism that limits the size of bedforms, these results confirm the existence of a robust relationship between the wavelength of large ripples and atmospheric density (ripples spacings increases with decreasing atmospheric density). This provides further support to the interpretation of paleoatmospheric conditions on Mars through the analysis of its aeolian sedimentary record.