Angle 

  • 1 Radian = 57.29578 Degrees 
  • 1 gradian = 0.9 degree = 0.015708 radian 

Length 

  • 1 feet = 0.3048 m = 0.3333 Yard 
  • 1 m = 3.281 feet = 39.37 inch = 1.0936 Yard 
  • 1 micron = 1 µm = 1.0 × 10^-6 m 
  • 1 angstrom = 1.0 × 10^ –10 m
  • 1 mil = 0.001 inch
  • 1 mile = 1760 Yard = 5280 feet = 1.6093 km
  • 1 Yard = 3 feet = 36 in = 0.9144 m
Area 
  • 1 acre = 43,560 sq. feet = 1/640 sq. mile = 0.40469 hectare (ha)
  • 1 darcy = 9.86923 × 10^ –13 sqm. (approx. the area of 1 micron × 1 micron)
  • 1 ha = 10,000 sqm. = 2.471 acres = 107,639 sq. feet = 0.00386 sq. mile
  • 1 sq. km = 247.105 acres = 100 ha = 1,195,990.05 sq. yard
  • 1 sq. mile = 640 acres = 259 ha
Volume 
  • 1 acre-feet = 43,560 cu.feet  = 325,851.43 gal (U.S.) 
  • 1 fl. oz. (U.S.) = 1/128 gal (U.S.) = 29.574 mL = 1.80469 cu.inch. 
  • 1 cu.feet = 7.4805 gal (U.S.) = 28.3168 L
  • 1 gal (Imperial) = 4.5461 L
  • 1 gal (U.S.) = 0.13368 cu.feet = 3.7854 L = 4 quarts = 8 pints = 16 cups
  • 1 L = 0.2642 gal (U.S.) = 0.03531 cu.feet
  • 1 gal (water) = 8.34 lb
  • 1 cu.feet (water) = 62.45 lb 
Velocity 
  • 1 mph = 1.46667 feet/s = 0.447 m/s = 1.609 kmph      (mph = Miles Per Hour)
  • 1 m/s = 3.281 feet/s = 3.6 kmph = 2.237 mph 
  •  Mach 1 (speed of sound at standard conditions) = 1225.1 kmph = 761.2 mph
Universal Constants
  • Acceleration due to gravity (g) = 9.80665 m/s^2 = 32.174 feet/s^2 
  • Atomic mass unit (mu = 1 u) = 1.66054 × 10^–27 kg 
  • Avogadro number (NA) = 6.022141 × 10^23 /mol 
  • Boltzmann constant (k) = 1.38065 × 10^–23 J/K 
  • Electric permittivity of free space (εo ) = 8.854187… × 10^–12 F/m 
  • Electron charge (e) = 1.602176 × 10^–19 C 
  • Electron rest mass (me ) = 9.109382 × 10^–31 kg 
  • Electron volt (eV) = 1.602176 × 10^–19 J 
  • Euler’s constant (γ) = 0.577215664901532… 
  • Faraday’s constant (F) = 96485.34 C/mol 
  • Gravitational constant (G) = 6.6738 × 10^–11 N-m^2 /kg^2 
  • Magnetic permeability of free space (µo ) = 4π × 10^–7 = 1.25664 × 10^–6 H/m 
  • Molar volume of an ideal gas (at 0°C) = 22.414 L 
  • Natural (Naperian) logarithm base (e) = 2.718281828459045… 
  • Pi (π) = 3.14159265358979… 
  • Planck constant (h) = 6.62607 × 10^–34 J-s 
  • Speed of light in vacuum (c) = 2.99792458 × 10^8 m/s 
  • Stefan-Boltzmann constant (σ) = 5.6704 × 10^–8 W/m^2 -K^4 
  • Universal gas constant (R) = 8.314462 J/mol-K