The surface pressure on Mars is about 10 millibars compared to typical earth pressures of 1013 millibars. The pressure scale height for the earth is about 8.5 kilometers so that at 8.5 kilometers the pressure is 1013/2.7 = 375 millibars, and that means that at about 4.5 pressure scale heights or 38 kilometers you are near 10 millibars.