Avogadro's number, N_A = 6.02214129 x 10²³ mol^-1

Faraday constant (F) = 9.6485 x 10⁴ C•mol^-1

Planck constant (h) = 6.62606957 x 10^-34 Joule•second

Boltzmann constant (k) = 1.3806488 x 10^-23 Joule•degree^-1

Speed of light (c) = 2.99792458 x 10¹⁰ cm•s^-1

Rydberg constant (R_h) = 13.60569253 eV = 109737.2573 cm^-1

1 Angstrom = 10^-8 cm = 10^-10 m

1 Bohr (a₀) = 0.52917721092 Angstroms 

1 amu = 1.6605402 x 10^-27 kg

1 electron charge = 1.602176565 x 10^-19 Coulombs

1 electron mass = 0.910938291 x 10^-30 kg  (electron rest mass m_e = 9.10953 x 10^-31 kg)

1 amu = 1822.8880 electron mass

1 proton mass = 1836.1527 electron mass

pressure
1 atm = 760 mm Hg = 760 Torr =14.696 lb•in^-2 = 101325 N•m^-2
          = 101325 Pa = = 101.325 kPa = 1.01325 bar = 1013.25 mb
1 atm = 14.696 psi = 1.033227 x 10⁴ kg•m^-2 = 1.033 kg•cm^-2 
1 bar = 100 kPa
1 Pa = 1 N•m^-2

force
1 N(newton) = 1 kg•m•s^-1  

temperature
T(K) = T(°C) + 273.15;  T(°F) = [9/5]T(°C) + 32;  

energy
1 Hartree = 27.21138505 eV = 627.5095 kcal•mol^-1 = 219474.6313 cm^-1;
1 eV = 8065.54 cm^-1 = 23.0605 kcal•mol^-1 = 1.602177 x 10^-12 erg;
1 erg =  10^-7 J
1 cal = 4.1840 J = 4.1840 x 10⁷ erg; 

 mass
1 kg = 2.205 lb;  1 lb = 453.59 g;

length
1 m = 39.37 in;  1 km = 0.6214 mi; 2.54 cm = 1 in

volume
1 L = 1.057 qt;   453.59237 g  = 1 lb;  28.35 g = 1 oz; 1 gal(gallon) = 3.785 gt; 1 L = 1000 mL = 1000 cm³

universal gas constant, R    [PV = nRT]
R = 0.082058 L•atm•mol^-1•K^-1 [when P is in atm]
    = 8.3145 J•mol^-1•K^-1 [when P is in Pa; V is in m³]
    = 62.364 Torr•mol^-1•K^-1 [when P is in Torr]