How to reduces Nested IF code(144 Nested IF) to achive same functionality

Hello, I am coding for Pressure units convertor in Excel2007, I have write the nested IF function about 144 nested IF function's levels, but Excel 2007 supports up to 64 nested functions, tell me the solution, How i reduce this code to achieve the same functionality or alternate of Nested If function that can achieve the same task.
Code is given below

Nested IF AND Function For Pressure Conversion
=IF(AND((G21="in.H2O"),(G22="in.H2O")),ROUNDUP((I21*1),2),IF(AND((G21="in.H2O"),(G22="in.Hg")),ROUNDUP((I21*0.07354),2),IF(AND((G21="in.H2O"),(G22="mmH2O")),ROUNDUP((I21*25.4),2),IF(AND((G21="in.H2O"),(G22="mmHg/Torr")),ROUNDUP((I21*1.868),2),IF(AND((G21="in.H2O"),(G22="Kg/Cm2")),ROUNDUP((I21*0.0025396),2),IF(AND((G21="in.H2O"),(G22="bar")),ROUNDUP((I21*0.002489),2),IF(AND((G21="in.H2O"),(G22="mbar")),ROUNDUP((I21*2.489),2),IF(AND((G21="in.H2O"),(G22="Pa")),ROUNDUP((I21*248.9),2),IF(AND((G21="in.H2O"),(G22="KPa")),ROUNDUP((I21*0.2489),2),IF(AND((G21="in.H2O"),(G22="MPa")),ROUNDUP((I21*0.0002489),2),IF(AND((G21="in.H2O"),(G22="PSI")),ROUNDUP((I21*0.03612),2), IF(AND((G21="in.H2O"),(G22="atm")),ROUNDUP((I21*0.00245832),2), IF(AND((G21="in.Hg"),(G22="in.H2O")),ROUNDUP((I21*13.598),2),IF(AND((G21="in.Hg"),(G22="in.Hg")),ROUNDUP((I21*1),2),IF(AND((G21="in.Hg"),(G22="mmH2O")),ROUNDUP((I21*345.315),2),IF(AND((G21="in.Hg"),(G22="mmHg/Torr")),ROUNDUP((I21*25.4),2),IF(AND((G21="in.Hg"),(G22="Kg/Cm2")),ROUNDUP((I21*0.034532),2),IF(AND((G21="in.Hg"),(G22="bar")),ROUNDUP((I21*0.03385),2),IF(AND((G21="in.Hg"),(G22="mbar")),ROUNDUP((I21*33.85),2),IF(AND((G21="in.Hg"),(G22="Pa")),ROUNDUP((I21*3385),2),IF(AND((G21="in.Hg"),(G22="KPa")),ROUNDUP((I21*3.385),2),IF(AND((G21="in.Hg"),(G22="MPa")),ROUNDUP((I21*0.003385),2), IF(AND((G21="in.Hg"),(G22="PSI")),ROUNDUP((I21*0.491154),2),IF(AND((G21="in.Hg"),(G22="atm")),ROUNDUP((I21*0.0334211),2),IF(AND((G21="mmH2O"),(G22="in.H2O")),ROUNDUP((I21*0.0393701),2),IF(AND((G21="mmH2O"),(G22="in.Hg")),ROUNDUP((I21*0.00289590),2),IF(AND((G21="mmH2O"),(G22="mmH2O")),ROUNDUP((I21*1),2),IF(AND((G21="mmH2O"),(G22="mmHg/Torr")),ROUNDUP((I21*0.0735559),2),IF(AND((G21="mmH2O"),(G22="Kg/Cm2")),ROUNDUP((I21*0.0001),2),IF(AND((G21="mmH2O"),(G22="bar")),ROUNDUP((I21*0.0000980665),2),IF(AND((G21="mmH2O"),(G22="mbar")),ROUNDUP((I21*0.0980665),2),IF(AND((G21=”mmH2O"),(G22="Pa")),ROUNDUP((I21*9.80665),2),IF(AND((G21="mmH2O"),(G22="KPa")),ROUNDUP((I21*0.00980665),2),IF(AND((G21="mmH2O"),(G22="MPa")),ROUNDUP((I21*0.00000980665),2),IF(AND((G21="mmH2O"),(G22="PSI")),ROUNDUP((I21*0.00142233),2),IF(AND((G21="mmH2O"),(G22="atm")),ROUNDUP((I21*0.0000967841),2),IF(AND((G21="mmHg/Torr"),(G22="in.H2O")),ROUNDUP((I21*0.5353),2),IF(AND((G21="mmHg/Torr"),(G22="in.Hg")),ROUNDUP((I21*0.03937),2),IF(AND((G21="mmHg/Torr"),(G22="mmH2O")),ROUNDUP((I21*13.5951),2),IF(AND((G21="mmHg/Torr"),(G22="mmHg/Torr")),ROUNDUP((I21*1),2),IF(AND((G21="mmHg/Torr"),(G22="Kg/Cm2")),ROUNDUP((I21*0.001359),2),IF(AND((G21="mmHg/Torr"),(G22="bar")),ROUNDUP((I21*0.00133),2),IF(AND((G21="mmHg/Torr"),(G22="mbar")),ROUNDUP((I21*1.3328),2),IF(AND((G21="mmHg/Torr"),(G22="Pa")),ROUNDUP((I21*133.28),2),IF(AND((G21="mmHg/Torr"),(G22="KPa")),ROUNDUP((I21*0.13328),2),IF(AND((G21="mmHg/Torr"),(G22="MPa")),ROUNDUP((I21*0.00013328),2),IF(AND((G21="mmHg/Torr"),(G22="PSI")),ROUNDUP((I21*0.01934),2),IF(AND((G21="mmHg/Torr"),(G22="atm")),ROUNDUP((I21*0.00131579),2), IF(AND((G21="Kg/Cm2"),(G22="in.H2O")),ROUNDUP((I21*393.76),2),IF(AND((G21="Kg/Cm2"),(G22="in.Hg")),ROUNDUP((I21*28.958),2),IF(AND((G21="Kg/Cm2"),(G22="mmH2O")),ROUNDUP((I21*10000),2),IF(AND((G21="Kg/Cm2"),(G22="mmHg/Torr")),ROUNDUP((I21*735.54),2),IF(AND((G21="Kg/Cm2"),(G22="Kg/Cm2")),ROUNDUP((I21*1),2),IF(AND((G21="Kg/Cm2"),(G22="bar")),ROUNDUP((I21*0.9804),2),IF(AND((G21="Kg/Cm2"),(G22="mbar")),ROUNDUP((I21*908.4),2),IF(AND((G21="Kg/Cm2"),(G22="Pa")),ROUNDUP((I21*98040),2),IF(AND((G21=”Kg/Cm2"),(G22="KPa")),ROUNDUP((I21*98.04),2),IF(AND((G21="Kg/Cm2"),(G22="MPa")),ROUNDUP((I21*0.09804),2),IF(AND((G21="Kg/Cm2"),(G22="PSI")),ROUNDUP((I21*14.223),2),IF(AND((G21="Kg/Cm2"),(G22="atm")),ROUNDUP((I21*0.967841),2),IF(AND((G21="bar"),(G22="in.H2O")),ROUNDUP((I21*401.65),2),IF(AND((G21="bar"),(G22="in.Hg")),ROUNDUP((I21*29.54),2),IF(AND((G21="bar"),(G22="mmH2O")),ROUNDUP((I21*10197.2),2),IF(AND((G21="bar"),(G22="mmHg/Torr")),ROUNDUP((I21*750),2),IF(AND((G21="bar"),(G22="Kg/Cm2")),ROUNDUP((I21*1.02),2),IF(AND((G21="bar"),(G22="bar")),ROUNDUP((I21*1),2),IF(AND((G21="bar"),(G22="mbar")),ROUNDUP((I21*1000),2),IF(AND((G21="bar"),(G22="Pa")),ROUNDUP((I21*100000),2),IF(AND((G21="bar"),(G22="KPa")),ROUNDUP((I21*100),2),IF(AND((G21="bar"),(G22="MPa")),ROUNDUP((I21*0.10),2),IF(AND((G21="bar"),(G22="PS")),ROUNDUP((I21*14.503861),2),IF(AND((G21="bar"),(G22="atm")),ROUNDUP((I21*0.986923),2),IF(AND((G21="mbar"),(G22="in.H2O")),ROUNDUP((I21*0.4018),2),IF(AND((G21="mbar"),(G22="in.Hg")),ROUNDUP((I21*0.02954),2),IF(AND((G21="mbar"),(G22="mmH2O")),ROUNDUP((I21*10.1972),2),IF(AND((G21="mbar"),(G22="mmHg/Torr")),ROUNDUP((I21*0.75028),2),IF(AND((G21="mbar"),(G22="Kg/Cm2")),ROUNDUP((I21*0.00102),2),IF(AND((G21="mbar"),(G22="bar")),ROUNDUP((I21*0.001),2),IF(AND((G21="mbar"),(G22="mbar")),ROUNDUP((I21*1),2),IF(AND((G21="mbar"),(G22="Pa")),ROUNDUP((I21*100),2),IF(AND((G21="mbar"),(G22="KPa")),ROUNDUP((I21*0.1),2),IF(AND((G21=" mbar"),(G22="MPa")),ROUNDUP((I21*0.0001),2), IF(AND((G21=" mbar"),(G22="PSI")),ROUNDUP((I21*0.0145),2),IF(AND((G21=" mbar"),(G22="atm")),ROUNDUP((I21*0.000986923),2),IF(AND((G21="Pa"),(G22="in.H2O")),ROUNDUP((I21*0.004018),2),IF(AND((G21="Pa"),(G22="in.Hg")),ROUNDUP((I21*0.0002954),2),IF(AND((G21="Pa"),(G22="mmH2O")),ROUNDUP((I21*0.101972),2),IF(AND((G21="Pa"),(G22="mmHg/Torr")),ROUNDUP((I21*0.0075),2),IF(AND((G21="Pa"),(G22="Kg/Cm2")),ROUNDUP((I21*0.0000102),2),IF(AND((G21="Pa"),(G22="bar")),ROUNDUP((I21*0.00001),2),IF(AND((G21="Pa"),(G22="mbar")),ROUNDUP((I21*0.01),2),IF(AND((G21="Pa"),(G22="Pa")),ROUNDUP((I21*1),2),IF(AND((G21="Pa"),(G22="KPa")),ROUNDUP((I21*0.001),2),IF(AND((G21="Pa"),(G22="MPa")),ROUNDUP((I21*0.000001),2),IF(AND((G21="Pa"),(G22="PSI")),ROUNDUP((I21*0.000145),2),IF(AND((G21="Pa"),(G22="atm")),ROUNDUP((I21*0.00000986923),2), IF(AND((G21=" KPa"),(G22="in.H2O")),ROUNDUP((I21*4.01463),2), IF(AND((G21="KPa"),(G22="in.Hg")),ROUNDUP((I21*0.295300),2),IF(AND((G21="Pa"),(G22="mmH2O")),ROUNDUP((I21*101.972),2),IF(AND((G21="KPa"),(G22="mmHg/Torr")),ROUNDUP((I21*7.50062),2),IF(AND((G21="KPa"),(G22="Kg/Cm2")),ROUNDUP((I21*0.0101972),2),IF(AND((G21="KPa"),(G22="bar")),ROUNDUP((I21*0.01),2),IF(AND((G21="KPa"),(G22="mbar")),ROUNDUP((I21*10),2),IF(AND((G21="KPa"),(G22="Pa")),ROUNDUP((I21*1000),2),IF(AND((G21=”KPa"),(G22="KPa")),ROUNDUP((I21*1),2),IF(AND((G21="KPa"),(G22="MPa")),ROUNDUP((I21*0.001),2),IF(AND((G21="KPa"),(G22="PSI")),ROUNDUP((I21*0.145038),2),IF(AND((G21="KPa"),(G22="atm")),ROUNDUP((I21*0.0098693),2),IF(AND((G21="MPa"),(G22="in.H2O")),ROUNDUP((I21*4014.63),2),IF(AND((G21="MPa"),(G22="in.Hg")),ROUNDUP((I21*295.3),2),IF(AND((G21="MPa"),(G22="mmH2O")),ROUNDUP((I21*101972),2),IF(AND((G21="MPa"),(G22="mmHg/Torr")),ROUNDUP((I21*7500.62),2),IF(AND((G21="MPa"),(G22="Kg/Cm2")),ROUNDUP((I21*10.1972),2),IF(AND((G21="MPa"),(G22="bar")),ROUNDUP((I21*10),2),IF(AND((G21="MPa"),(G22="mbar")),ROUNDUP((I21*10000),2),IF(AND((G21="MPa"),(G22="Pa")),ROUNDUP((I21*1000000),2),IF(AND((G21="MPa"),(G22="KPa")),ROUNDUP((I21*1000),2),IF(AND((G21="MPa"),(G22="MPa")),ROUNDUP((I21*1),2),IF(AND((G21="MPa"),(G22="PSI")),ROUNDUP((I21*145.038),2),IF(AND((G21=" MPa"),(G22="atm")),ROUNDUP((I21*9.86923),2), IF(AND((G21="PSI"),(G22="in.H2O")),ROUNDUP((I21*27.71),2),IF(AND((G21="PSI"),(G22="in.Hg")),ROUNDUP((I21*2.036),2),IF(AND((G21="PSI"),(G22="mmH2O")),ROUNDUP((I21*703.1),2),IF(AND((G21="PSI"),(G22="mmHg/Torr")),ROUNDUP((I21*51.75),2),IF(AND((G21="PSI"),(G22="Kg/Cm2")),ROUNDUP((I21*0.703),2),IF(AND((G21="PSI"),(G22="bar")),ROUNDUP((I21*0.689),2),IF(AND((G21="PSI"),(G22="mbar")),ROUNDUP((I21*68.95),2),IF(AND((G21="PSI"),(G22="Pa")),ROUNDUP((I21*6895),2),IF(AND((G21="PSI"),(G22="KPa")),ROUNDUP((I21*6.895),2),IF(AND((G21="PSI"),(G22="MPa")),ROUNDUP((I21*0.006895),2),IF(AND((G21="PSI"),(G22="PSI")),ROUNDUP((I21*1),2),IF(AND((G21="PSI"),(G22="atm")),ROUNDUP((I21*0.0680460),2),IF(AND((G21="atm"),(G22="in.H2O")),ROUNDUP((I21*406.86),2),IF(AND((G21="atm"),(G22="in.Hg")),ROUNDUP((I21*29.9213),2),IF(AND((G21="atm"),(G22="mmH2O")),ROUNDUP((I21*10332.3),2),IF(AND((G21="atm"),(G22="mmHg/Torr")),ROUNDUP((I21*760),2),IF(AND((G21="atm"),(G22="Kg/Cm2")),ROUNDUP((I21*1.03325),2),IF(AND((G21="atm"),(G22="bar")),ROUNDUP((I21*1.01325),2),IF(AND((G21”atm"),(G22="mbar")),ROUNDUP((I21*1012.95),2),IF(AND((G21="atm"),(G22="Pa")),ROUNDUP((I21*101325),2),IF(AND((G21="atm"),(G22="KPa")),ROUNDUP((I21*101.325),2),IF(AND((G21="atm"),(G22="MPa")),ROUNDUP((I21*0.101325),2),IF(AND((G21="atm"),(G22="PSI")),ROUNDUP((I21*14.7),2),IF(AND((G21="atm"),(G22="atm")),ROUNDUP((I21*1),2), ("Select Regtrd Unit")))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

Hello,
Your suggestion support well,
Thanks