Here is a list of useful constants, etc.:

Length:

• 1 inch = 2.54 cm
• 1 mile = 1.6 km
• 1 km = 1000 m
• 1 m = 100 cm = 1000 mm = 10⁹ nm
• Planck Legnth = 1.616252×10^-35 m = sqrt (h_bar G/c³)
• Classical Electron Radius = 2.81794×10^-15 m = e²/ m_e c²
• Proton Radius = 0.83×10^-15 m = 0.83 femtometer = 0.83×10^-13 cm
• 1 Angstrom = 10^-10 m = 10^-8 cm
• 1 Earth Radius = 6.37814×10⁸ cm = 6.37814×10⁶ m (Equatorial)
• 1 Jupiter Radius = 7.1492×10⁹ cm = 7.1492×10⁷ m (Equatorial)
• 1 Solar Radius = 6.9599¹⁰ cm = 6.9599×10⁸ m (Equatorial)
• 1 Moon’s Mean Orbital Radius = 384,400 km = 3.8440×10⁸ m
• 1 AU = 1.4960×10¹¹ m = 1.4960×10⁸ km (Astronomical Unit)
• 1 ly = 9.4605×10¹⁵ m = 9.4605×10¹² km (light year)
• 1 pc = 3.0857×10¹⁶ m = 3.0857×10¹³ km = 3.261633 ly = 206264.806 AU (parsec) = 3.0857×10¹⁸ cm
• 1 Mpc = 10⁶ pc (Megaparsec) = 3.0857×10²⁴ cm
• D_H = c/H0 = 3000 h^-1 Mpc = 9.26×10²⁷ h^-1 cm (The Hubble Scale)

Angles:

• 1° = 1 degree = 60′ = 60 arcminutes
• 1′ = 60″ = 60 arcseconds
• 1 radian = 360° /2 pi = 57.2957795131° = 206264.806″
• Area of a Sphere = 41252.96124 square degrees = 4 pi Steradians

Mass:

• 1 amu = 1.6605402 x10^-24 gram = 1.6605402 x10^-27 kg
• 1 amu c² = 931.49432 MeV
• 1 Hydrogen Atom Mass = 1.007825 amu = 1.673534 x10^-24 gram
• 1 Helium 4 Atom Mass = 4.00260325415 amu
• 1 Carbon 12 Atom Mass = 12.0000000 amu
• 1 Proton Mass = 1.6726231 x10^-24 gram
• 1 Neutron Mass = 1.674920 x10^-24 gram
• 1 Electron Mass = 9.1093897 x10^-28 gram
• 1 kg = 2.20462 lb
• 1 Solar Mass = 1.989×10³³ gram = 1.989×10³⁰ kg
• 1 Jupiter Mass = 1.899×10³⁰ gram = 1.899×10²⁷ kg
• 1 Earth Mass = 5.9736×10²⁷ gram = 5.9736×10²⁴ kg
• 1 Lunar Mass = 7.3477×10²⁵ gram = 7.3477×10²² kg
• (Proton Mass)/(Electron Mass) = 1836.15
• Earth’s Mean Density = 5515.3 kg/m³
• Moon’s Mean Density = 3346.4 kg/m³

Time:

• 1 Planck Time = 5.39124×10^-44 s = sqrt (h_bar G/c⁵)
• 1 Sidereal Day = 23^h 56^m 04.09054^s
• 1 Solar Day = 24^h = 86400 s
• 1 Sidereal Year = 3.155815×10⁷ s
• 1 Tropical Year = 3.155693×10⁷ s

Energy:

• 1 Joule = 2.39×10^-1 calorie
• 1 Joule = 10⁷ ergs
• 1 eV = 1.602177×10^-12 erg = 1.602177×10^-19 Joule
• 1 Solar Luminosity = 3.826×10³³ ergs/s = 3.826×10²⁶ Joules/s = 3.826×10²⁶ Watts
• Sun’s Absolute Magnitude V = 4.83, B = 5.48, K = 3.28
• Vega’s Absolute Magnitude V = 0.58, B = 0.58, K = 0.58

Temperature:

• Solar Surface Effective Temperature = 5770 K

Physical Constants:

• Avogadro’s Number = N_A = 6.0221367×10²³ /mole
• Gravitational Constant = G = 6.67259×10^-8 cm³ gram^-1 s^-2 = 4.301×10^-9 km² Mpc M_Sun^-1 s^-2
• Planck’s Constant = h = 6.6260755×10^-27 erg s
• Speed of Light = c = 2.99792458×10¹⁰ cm s^-1 = 2.99792458×10⁸ m s^-1
• Boltzmann’s Constant = k = 1.380658×10^-16 erg K^-1
• Stefan-Boltzmann Constant = σ = 5.67051×10^-5 erg cm^-2 K^-4 s^-1
• Radiation Density Constant = a = 7.56591×10^-15 erg cm^-3 K^-4
• Rydberg = R_H = 1.09677585×10 ⁵ cm^-1
• Electron charge = e = 4.8032×10^-10 esu = 1.6022×10^-19 Coulomb
• 1 Coulomb = 6.24151×10¹⁸ e