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Yahoo has links to web pages of constants and units.

The National Institute of Standards and Technology (NIST) has a page on the fundamental physical constants, a page on SI units, and a page with chemistry
data for chemical species.

Tech Expo has a page on fundamental constants

Various astronomical constants.

Conversion of units.

Conversion of units.

Yahoo
links to web pages that convert units.

Note that the absence of Greek letters on the web means some of the following symbols aren't quite right. Superscripts are prefixed with "^" to insure they can be interpreted correctly even if your browser does not support superscripts.

- Y: 10
^{^24}yotta - Z: 10
^{^21}zetta - E: 10
^{^18}exa - P: 10
^{^15}peta - T: 10
^{^12}tera - G: 10
^{^9}giga - M: 10
^{^6}mega - k: 10
^{^3}kilo - h: 10
^{^2}hecto - da: 10
^{^1}deka - d: 10
^{^-1}deci - c: 10
^{^-2}centi - m: 10
^{^-3}milli - mu: 10
^{^-6}micro - n: 10
^{^-9}nano - p: 10
^{^-12}pico - f: 10
^{^-15}femto - a: 10
^{^-18}atto - z: 10
^{^-21}zepto - y: 10
^{^-24}yocto

- m: meters (length)
- kg: kilogram (mass)
- s: seconds (time)
- A: ampere (electric current)
- K: kelvin (thermodynamic temperature)
- mol: mole (amount of substance)
- cd: candela (luminous intensity)

- J: joules (work, energy, heat) N*m, Kg*m
^{^2}/s^{^2} - N: newton, (force) kg*m/(s
^{^2}) - Pa: pascal, (pressure, stress) N/m
^{^2} - W: watt, (power) J/s
- C: coulomb, (electric charge) A*s
- V: volt (electric potential, emf) J/C, W/A
- Greek omega: ohm (resistance) V/A
- S: siemens (conductance) A/V
- Wb: weber (magnetic flux) V*s
- H: henry (inductance) Wb/A
- F: farad (capacitance) C/V
- T: Tesla (magnetic flux density) Wb/m
^{^2}, N/(A*m) - Bq: becquerel (radioactivity) 1/s

- c: 299,792,458 m/s; speed of light in vacuum[1]
- mu
_{0}: 12.566 370 614... x 10^{^-7}N/A^{^2}; Permeability of vacuum[1] - e
_{0}: 8.854 187 817 x 10^{^-12}F/m, or 1/(mu0 * c^{^2}); permittivity of vacuum[1] - G: 6.672 59 x 10
^{^-11}m^{^3}/(kg*s^{^2}); Newtonian constant of gravitation[1] - h: 6.626 075 5 x 10
^{^-34}J*s; Planck's constant[1] - e: 1.602 176 565 x 10
^{^-19}C; elementary charge on proton, electron[http://physics.nist.gov/cgi-bin/cuu/Value?e] - a
_{0}: 0.529 177 249 x 10^{^-10}m; Bohr radius [1] - E
_{h}: 4.359 748 2 x 10^{^-18}J; Hartree (energy)[1] - m
_{e}: 9.109 389 7 x 10^{^-31}kg; mass of the electron[1] - m
_{p}: 1.672 623 1 x 10^{^-27}kg; mass of the proton[1] - m
_{n}: 1.674 928 6 x 10^{^-27}kg; mass of the neutron[1] - N
_{A}: 6.022 141 29 x 10^{^23}mol^{^-1}; Avogadro's number [http://physics.nist.gov/cgi-bin/cuu/Value?na] - mu: 1.660 540 2 x 10
^{^-27}kg; atomic mass constant, amu[1] - R: 8.314 510 J/(mol*K); molar gas constant[1]
- k: 1.380 658 x 10
^{^-23}J/K; Boltzmann's constant R/N_{A}[1] - V
_{m}: 0.022 414 10 m^{^3}/mol; molar volume of ideal gas, R*T/p at 273.15 K, 101,325 Pa[1] - Volume occupied by one gas molecule at STP: ~37.22 nm
^{^3}(V_{m}/ N_{A}) - lattice spacing of diamond (300 K): 0.356 683 nm[5]
- lattice spacing of silicon (300 K): 0.543 095 nm[5]
- lattice spacing of germanium (300 K): 0.564 613 nm[5]
- lattice spacing of grey tin (300 K): 0.648 920 nm[5]
- C-C bond length in diamond: 0.154 448 nm it's the lattice spacing * sqrt(3)/4
- C-C bond length in graphite: 0.142 nm [9]
- 1-3 distance in graphite: 0.246 nm; C-C bond length * sqrt(3)
- density of carbon atoms in a monoatomic sheet of graphite: 38.2 atoms/nm
^{2}; 4/( (C-C bond length)^{2}*3*sqrt(3))) - Distance between adjacent sheets in graphite: 0.335 nm [9]
- Basal surface energy of graphite: 0.234 J/m
^{2}[9] - bandgap of diamond: 5.47 eV[5]
- bandgap of silicon: 1.12 eV[5]
- mobility of electron in diamond: 1800 cm
^{^2}/(V*s)[5] - mobility of electron in silicon: 1500 cm
^{^2}/(V*s)[5] - g
_{n}: 9.806 65 m/s^{^2}; acceleration of gravity[1] - Solar constant: 1,367.5 W/m
^{^2}; number of watts in sunlight near Earth's orbit, variable with Earth's distance from the sun and solar activity[8] - Solar output: 3.87 x 10
^{^26}W (computed from solar constant)[3] - Typical power consumption of a human being: ~100 W
- Energy used by the United States in 1990: 8.6 x 10
^{^19}J[6] - Energy used per person per year in the US in 1990: 3.5 x 10
^{^11}J[6] - Power used per person in the US in 1990: 11,000 W (computed from above)
- Energy used by the world in 1990: 1.4 x 10
^{^20}J[6] - Power consumption of the world in 1990: 4.4 x 10
^{^12}W (computed from above) - Energy used per person per year in the world in 1990: 2.7 x 10
^{^10}J[6] - Power used per person in the world in 1990: 850 W (computed from above)
- Total world population in 1990: 5.3 x 10
^{^9}[6] - Earth's equatorial radius: 6,378,160 m [3]
- Earth's surface area (4 pi r
^{^2}, r from above): 5.1 x 10^{^14}m^{^2} - Solar power intercepted by the Earth: 1.74 x 10
^{^17}W (derived from above) - Earth's mass: 5.975 x 10
^{^24}kg[3] - Earth's distance from sun (average): 1.5 x 10
^{^11}m[3] - Fraction of nitrogen in Earth's atmosphere (by volume): 0.780 84[3]
- Fraction of oxygen in Earth's atmosphere (by volume): 0.209 46[3]
- Fraction of water in Earth's atmosphere: variable. Arctic air might have 0.01% water by weight while tropical air might have 3%.
- Fraction of argon in Earth's atmosphere (by volume): 0.00934[3]
- Fraction of CO2 in Earth's atmosphere (by volume): 0.00031[3]
- More information about the earth
- Stiffness of carbon-carbon single bond: 440 N/m[4]
- Energy required to break carbon-carbon single bond: 0.556 aJ[4]
- Young's modulus of diamond: 1.05 x 10
^{^12}Pa - Strength of diamond: 5 x 10
^{^10}Pa (an underestimate)[4] - Density of diamond: 3500 kg/m
^{^3}[4]

- one atmosphere (atm) is 101,325 Pa[1]
- one calorie (cal) is 4.184 J[2]
- one joule (J) is 0.0002390057361 kcal (derived from above)
- one joule is (J) 1.439325215 x 10
^{^20}kcal/mole (derived from above) - one eV is 96.48533646 kJ/mol (derived from above)
- one kcal/mole is 6.947700141 x 10
^{^-21}J (derived from above) - one Hartree is 627.5095 Kcal/mol is 27.2116 eV is 4.3597482 x 10
^{^-18}J[2] - one electron volt (eV) is 1.602 176 565 x 10
^{^-19}J[http://physics.nist.gov/cgi-bin/cuu/Value?e] - 1,000 kg of crude oil is about 7.3 barrels
- one barrel is 158.9873 liters [7]