Inside the CAS, all derived units are stored using the MKSA system. This of course can lead to some small rounding errors in conversions from US units to US units, it's unavoidable (and in is a reserved word inside the CAS, so that you can loop in a list, you must use inch for the unit. Since inch is not a metric unit, it has no real reason to have a reserved word).
First number is a numeric factor, remainding numbers are powers of meter, kilogram, second, Ampere, Kelvin, mol, candela, last column is reserved for currency conversions.
Code:
const mksa_unit __Angstrom_unit={1e-10,1,0,0,0,0,0,0,0};
const mksa_unit __Btu_unit={1055.05585262,2,1,-2,0,0,0,0,0};
const mksa_unit __Curie_unit={3.7e10,0,0,-1,0,0,0,0,0};
const mksa_unit __FF_unit={.152449017237,0,0,0,0,0,0,0,1};
const mksa_unit __Fdy_unit={96485.3365,0,0,1,1,0,0,0,0};
const mksa_unit __Gal={0.01,1,0,-2,0,0,0,0,0};
const mksa_unit __HFCC_unit={1400,1,0,0,0,0,0,0,0};
const mksa_unit __L_unit={0.001,3,0,0,0,0,0,0,0};
const mksa_unit __P_unit={.1,-1,1,-1,0,0,0,0,0};
const mksa_unit __R_unit={0.000258,0,-1,1,1,0,0,0,0};
const mksa_unit __Rankine_unit={5./9,0,0,0,0,1,0,0,0};
const mksa_unit __St_unit={0.0001,2,0,-1,0,0,0,0,0};
const mksa_unit __Wh_unit={3600,2,1,-2,0,0,0,0,0};
const mksa_unit __a_unit={100,2,0,0,0,0,0,0,0};
const mksa_unit __acre_unit={4046.87260987,2,0,0,0,0,0,0,0};
const mksa_unit __arcmin_unit={2.90888208666e-4,0,0,0,0,0,0,0,0};
const mksa_unit __arcs_unit={4.8481368111e-6,0,0,0,0,0,0,0,0};
const mksa_unit __atm_unit={101325.0,-1,1,-2,0,0,0,0,0};
const mksa_unit __au_unit={1.495979e11,1,0,0,0,0,0,0,0};
const mksa_unit __b_unit={1e-28,2,0,0,0,0,0,0,0};
const mksa_unit __bar_unit={1e5,-1,1,-2,0,0,0,0,0};
const mksa_unit __bbl_unit={.158987294928,3,0,0,0,0,0,0,0};
const mksa_unit __bblep_unit={.158987294928*0.857*41.76e9,2,1,-2,0,0,0,0,0};
const mksa_unit __boe_unit={.158987294928*0.857*41.76e9,2,1,-2,0,0,0,0,0};
const mksa_unit __bu={0.036368736,3,0,0,0,0,0,0,0};
const mksa_unit __buUS={0.03523907,3,0,0,0,0,0,0,0};
const mksa_unit __cal_unit={4.1868,2,1,-2,0,0,0,0,0};
const mksa_unit __cf_unit={1.08e6,2,1,-2,0,0,0,0,0};
const mksa_unit __chain_unit={20.1168402337,1,0,0,0,0,0,0,0};
const mksa_unit __ct_unit={0.0002,0,1,0,0,0,0,0,0};
const mksa_unit __dB_unit={1,0,0,0,0,0,0,0,0};
const mksa_unit __d_unit={86400,0,0,1,0,0,0,0,0};
const mksa_unit __deg_unit={1.74532925199e-2,0,0,0,0,0,0,0,0};
// const mksa_unit __degreeF_unit={5./9,0,0,0,0,1,0,0,0};
const mksa_unit __dyn_unit={1e-5,1,1,-2,0,0,0,0,0};
const mksa_unit __eV_unit={1.60217733e-19,2,1,-2,0,0,0,0,0};
const mksa_unit __erg_unit={1e-7,2,1,-2,0,0,0,0,0};
const mksa_unit __fath_unit={1.82880365761,1,0,0,0,0,0,0,0};
const mksa_unit __fbm_unit={0.002359737216,3,0,0,0,0,0,0,0};
const mksa_unit __fc_unit={10.7639104167,1,0,0,0,0,0,0,0};
const mksa_unit __fermi_unit={1e-15,1,0,0,0,0,0,0,0};
const mksa_unit __flam_unit={3.42625909964,-2,0,0,0,0,0,1,0};
const mksa_unit __fm_unit={1.82880365761,1,0,0,0,0,0,0,0};
const mksa_unit __ft_unit={0.3048,1,0,0,0,0,0,0,0};
const mksa_unit __ftUS_unit={0.304800609601,1,0,0,0,0,0,0,0};
const mksa_unit __g_unit={1e-3,0,1,0,0,0,0,0,0};
const mksa_unit __galC_unit={0.00454609,3,0,0,0,0,0,0,0};
const mksa_unit __galUK_unit={0.004546092,3,0,0,0,0,0,0,0};
const mksa_unit __galUS_unit={0.003785411784,3,0,0,0,0,0,0,0};
const mksa_unit __cu_unit={0.000236588236373,3,0,0,0,0,0,0,0};
const mksa_unit __gf_unit={0.00980665,1,1,-2,0,0,0,0,0};
const mksa_unit __gmol_unit={1,0,0,0,0,0,1,0,0};
const mksa_unit __gon_unit={1.57079632679e-2,0,0,0,0,0,0,0};
const mksa_unit __grad_unit={1.57079632679e-2,0,0,0,0,0,0,0,0};
const mksa_unit __grain_unit={0.00006479891,0,1,0,0,0,0,0,0};
const mksa_unit __h_unit={3600,0,0,1,0,0,0,0,0};
const mksa_unit __ha_unit={10000,2,0,0,0,0,0,0,0};
const mksa_unit __hp_unit={745.699871582,2,1,-3,0,0,0,0,0};
const mksa_unit __in_unit={0.0254,1,0,0,0,0,0,0,0};
const mksa_unit __inH2O_unit={248.84,-1,1,-2,0,0,0,0,0};
const mksa_unit __inHg_unit={3386.38815789,-1,1,-2,0,0,0,0,0};
const mksa_unit __j_unit={86400,0,0,1,0,0,0,0,0};
const mksa_unit __kip_unit={4448.22161526,1,1,-2,0,0,0,0,0};
const mksa_unit __knot_unit={0.51444444444,1,0,-1,0,0,0,0,0};
const mksa_unit __kph_unit={0.2777777777777,1,0,-1,0,0,0,0,0};
const mksa_unit __l_unit={0.001,3,0,0,0,0,0,0,0};
const mksa_unit __lam_unit={3183.09886184,-2,0,0,0,0,0,1,0};
const mksa_unit __lb_unit={0.45359237,0,1,0,0,0,0,0,0};
const mksa_unit __lbf_unit={4.44922161526,1,1,-2,0,0,0,0,0};
const mksa_unit __lbmol_unit={453.59237,0,0,0,0,0,1,0,0};
const mksa_unit __lbt_unit={0.3732417216,0,1,0,0,0,0,0,0};
const mksa_unit __lep_unit={0.857*41.76e6,2,1,-2,0,0,0,0,0};
const mksa_unit __liqpt_unit={0.000473176473,3,0,0,0,0,0,0,0};
const mksa_unit __lyr_unit={9.46052840488e15,1,0,0,0,0,0,0,0};
const mksa_unit __mi_unit={1609.344,1,0,0,0,0,0,0,0};
const mksa_unit __miUS_unit={1609.34721869,1,0,0,0,0,0,0,0};
const mksa_unit __mil_unit={0.0000254,1,0,0,0,0,0,0,0};
const mksa_unit __mile_unit={1609.344,1,0,0,0,0,0,0,0};
const mksa_unit __mille_unit={1852,1,0,0,0,0,0,0,0};
const mksa_unit __mn_unit={60,0,0,1,0,0,0,0,0};
const mksa_unit __mmHg_unit={133.322368421,-1,1,-2,0,0,0,0,0};
const mksa_unit __molK_unit={1,0,0,0,0,1,1,0,0};
const mksa_unit __mph_unit={0.44704,1,0,-1,0,0,0,0,0};
const mksa_unit __nmi_unit={1852,1,0,0,0,0,0,0,0};
const mksa_unit __oz_unit={0.028349523125,0,1,0,0,0,0,0,0};
const mksa_unit __ozUK_unit={2.8413075e-5,3,0,0,0,0,0,0,0};
const mksa_unit __ozfl_unit={2.95735295625e-5,3,0,0,0,0,0,0,0};
const mksa_unit __ozt_unit={0.0311034768,0,1,0,0,0,0,0,0};
const mksa_unit __pc_unit={3.08567818585e16,1,0,0,0,0,0,0,0};
const mksa_unit __pdl_unit={0.138254954376,1,1,-2,0,0,0,0,0};
const mksa_unit __pk_unit={0.0088097675,3,0,0,0,0,0,0,0};
const mksa_unit __psi_unit={6894.75729317,-1,1,-2,0,0,0,0,0};
const mksa_unit __pt_unit={0.000473176473,3,0,0,0,0,0,0,0};
const mksa_unit __ptUK_unit={0.0005682615,3,0,0,0,0,0,0,0};
const mksa_unit __qt_unit={0.000946359246,3,0,0,0,0,0,0,0};
const mksa_unit __rd_unit={0.01,2,0,-2,0,0,0,0,0};
const mksa_unit __rem_unit={0.01,2,0,-2,0,0,0,0,0};
const mksa_unit __rod_unit={5.02921005842,1,0,0,0,0,0,0,0};
const mksa_unit __rpm_unit={0.0166666666667,0,0,-1,0,0,0,0,0};
const mksa_unit __sb_unit={10000,-2,0,0,0,0,0,1,0};
const mksa_unit __slug_unit={14.5939029372,0,1,0,0,0,0,0,0};
const mksa_unit __st_unit={1,3,0,0,0,0,0,0,0};
const mksa_unit __t_unit={1000,0,1,0,0,0,0,0,0};
const mksa_unit __tbsp_unit={1.47867647813e-5,3,0,0,0,0,0,0,0};
const mksa_unit __tec_unit={41.76e9/1.5,2,1,-2,0,0,0,0,0};
const mksa_unit __tep_unit={41.76e9,2,1,-2,0,0,0,0,0};
const mksa_unit __tepC_unit={830,1,0,0,0,0,0,0,0};
const mksa_unit __tepcC_unit={1000,1,0,0,0,0,0,0,0};
const mksa_unit __tepgC_unit={650,1,0,0,0,0,0,0,0};
const mksa_unit __tex={1e-6,-1,1,0,0,0,0,0,0};
const mksa_unit __therm_unit={105506000,2,1,-2,0,0,0,0,0};
const mksa_unit __toe_unit={41.76e9,2,1,-2,0,0,0,0,0};
const mksa_unit __ton_unit={907.18474,0,1,0,0,0,0,0,0};
const mksa_unit __tonUK_unit={1016.0469088,0,1,0,0,0,0,0,0};
const mksa_unit __torr_unit={133.322368421,-1,1,-2,0,0,0,0,0};
const mksa_unit __tr_unit={2*M_PI,0,0,0,0,0,0,0,0};
const mksa_unit __tsp_unit={4.928921614571597e-6,3,0,0,0,0,0,0,0};
const mksa_unit __u_unit={1.6605402e-27,0,1,0,0,0,0,0,0};
const mksa_unit __yd_unit={0.9144,1,0,0,0,0,0,0,0};
const mksa_unit __yr_unit={31556925.9747,0,0,1,0,0,0,0,0};
const mksa_unit __micron_unit={1e-6,1,0,0,0,0,0,0,0};
const mksa_unit __hbar_unit={1.05457266e-34,2,1,-1,0,0,0,0};
const mksa_unit __c_unit={299792458,1,0,-1,0,0,0,0};
const mksa_unit __g__unit={9.80665,1,0,-2,0,0,0,0};
const mksa_unit __IO_unit={1e-12,0,1,-3,0,0,0,0};
const mksa_unit __epsilonox_unit={3.9,0,0,0,0,0,0,0};
const mksa_unit __epsilonsi_unit={11.9,0,0,0,0,0,0,0,0};
const mksa_unit __qepsilon0_unit={1.4185979e-30,-3,-1,5,3,0,0,0};
const mksa_unit __epsilon0q_unit={55263469.6,-3,-1,3,1,0,0,0};
const mksa_unit __kq_unit={8.617386e-5,2,1,-3,-1,-1,0,0};
const mksa_unit __c3_unit={.002897756,1,0,0,0,1,0,0};
const mksa_unit __lambdac_unit={ 0.00242631058e-9,1,0,0,0,0,0,0,0};
const mksa_unit __f0_unit={2.4179883e14,0,0,-1,0,0,0,0};
const mksa_unit __lambda0_unit={1239.8425e-9,1,0,0,0,0,0,0};
const mksa_unit __muN_unit={5.0507866e-27,2,0,0,1,0,0,0};
const mksa_unit __muB_unit={ 9.2740154e-24,2,0,0,1,0,0,0};
const mksa_unit __a0_unit={.0529177249e-9,1,0,0,0,0,0,0};
const mksa_unit __Rinfinity_unit={10973731.534,-1,0,0,0,0,0,0};
const mksa_unit __Faraday_unit={96485.309,0,0,1,1,0,-1,0};
const mksa_unit __phi_unit={2.06783461e-15,2,1,-2,-1,0,0,0};
const mksa_unit __alpha_unit={7.29735308e-3,0,0,0,0,0,0,0};
const mksa_unit __mpme_unit={1836.152701,0,0,0,0,0,0,0};
const mksa_unit __mp_unit={1.6726231e-27,0,1,0,0,0,0,0};
const mksa_unit __qme_unit={1.75881962e11,0,-1,1,1,0,0,0};
const mksa_unit __me_unit={9.1093897e-31,0,1,0,0,0,0,0};
const mksa_unit __qe_unit={1.60217733e-19,0,0,1,1,0,0,0};
const mksa_unit __h__unit={6.6260755e-34,2,1,-1,0,0,0,0};
const mksa_unit __G_unit={6.67259e-11,3,-1,-2,0,0,0,0};
const mksa_unit __mu0_unit={1.25663706144e-6,1,1,-2,-2,0,0,0};
const mksa_unit __epsilon0_unit={8.85418781761e-12,-3,-1,4,2,0,0,0};
const mksa_unit __sigma_unit={ 5.67051e-8,0,1,-3,0,-4,0,0};
const mksa_unit __StdP_unit={101325.0,-1,1,-2,0,0,0,0};
const mksa_unit __StdT_unit={273.15,0,0,0,0,1,0,0};
const mksa_unit __R__unit={8.31451,2,1,-2,0,-1,-1,0};
const mksa_unit __Vm_unit={22.4141e-3,3,0,0,0,0,-1,0};
const mksa_unit __k_unit={1.380658e-23,2,1,-2,0,-1,0,0};
const mksa_unit __NA_unit={6.0221367e23,0,0,0,0,0,-1,0};
const mksa_unit __mSun_unit={1.989e30,0,1,0,0,0,0,0};
const mksa_unit __RSun_unit={6.955e8,1,0,0,0,0,0,0};
const mksa_unit __PSun_unit={3.846e26,2,1,-3,0,0,0,0};
const mksa_unit __mEarth_unit={5.9736e24,0,1,0,0,0,0,0};
const mksa_unit __REarth_unit={6.371e6,1,0,0,0,0,0,0};
const mksa_unit __sd_unit={8.61640905e4,0,0,1,0,0,0,0};
const mksa_unit __syr_unit={3.15581498e7,0,0,1,0,0,0,0};