Copyright Goodheart-Willcox Co., Inc. May not be reproduced or posted to a publicly accessible website. 88 Math for HVACR To convert from pounds per square inch (psi) to inches of mercury (in. Hg), the conversion chart shows a multiplier of 2.036. Thus, to convert 40 psi to in. Hg, the calculation would be as shown. 40 psi × 2.036 = 81.44 in. Hg Thus, 40 psi equals 81.44 in. Hg. To convert from in. Hg to psi, the multiplier shown is 0.4912. 81.44 in. Hg × 0.4912 = 40.003328 psi Thus, 81.44 in. Hg equals 40.003328 psi, which can be rounded to 40 psi. Conversion Factors for Pressure Measurements of the SI System Multiply: by To obtain: bar 100 kilopascal (kPa) bar 1,000 millibar (mb) bar 1.02 kilogram/centimeter2 (kg/cm2) kilopascal (kPa) 0.01 bar kilopascal (kPa) 10 millibar (mb) kilopascal (kPa) 1,000 pascal (Pa) kilogram/centimeter2 (kg/cm2) 980.7 millibar (mb) kilogram/centimeter2 (kg/cm2) 0.9807 bar kilogram/centimeter2 (kg/cm2) 98.07 kilopascal (kPa) kilogram/centimeter2 (kg/cm2) 735.6 millimeter of mercury (torr) millibar (mb) 0.001 bar millibar (mb) 0.1 kilopascal (kPa) millibar (mb) 100 pascal (Pa) millibar (mb) 0.00102 kilogram/centimeter2 (kg/cm2) millibar (mb) 0.7501 millimeter of mercury (torr) millimeter of mercury (torr) 1.333 millibar (mb) millimeter of mercury (torr) 133.3 pascal (Pa) millimeter of mercury (torr) 0.1333 kilopascal (kPa) millimeter of mercury (torr) 0.00136 kilogram/centimeter2 (kg/cm2) pascal (Pa) 1 newton/square meter (N/m2) pascal (Pa) 0.001 kilopascal (kPa) pascal (Pa) 0.0000102 kilogram/centimeter2 (kg/cm2) pascal (Pa) 0.00001 bar pascal (Pa) 0.01 millibar (mb) pascal (Pa) 0.007501 millimeter of mercury (torr) Goodheart-Willcox Publisher