# Physical Constants, Prefixes, and Conversion Factors

Here are some useful physical constants, conversion factors, and unit prefixes. They are used in many calculations in chemistry, as well as in physics and other sciences.

Useful Constants

 Acceleration of Gravity 9.806 m/s2 Avogadro’s Number 6.022 x 1023 Electronic Charge 1.602 x 10-19 C Faraday Constant 9.6485 x 104 J/V Gas Constant 0.08206 L·atm/(mol·K)8.314 J/(mol·K)8.314 x 107 g·cm2/(s2·mol·K) Planck’s Constant 6.626 x 10-34 J·s Speed of Light 2.998 x 108 m/s p 3.14159 e 2.718 ln x 2.3026 log x 2.3026 R 19.14 J/(mol·K) 2.3026 RT (at 25°C) 5.708 kJ/mol

Common Conversion Factors

QuantitySI UnitOther UnitConversion Factor
Energyjoulecalorie
erg
1 cal = 4.184 J
1 erg = 10-7 J
Forcenewtondyne1 dyn = 10-5 N
LengthmetreAngstrom1 Å = 10-10 m = 10-8 cm = 10-1 nm
Masskilogrampound1 lb = 0.453592 kg
Pressurepascalbar
atmosphere
mm Hg
lb/in2
1 bar = 105 Pa
1 atm = 1.01325 x 105 Pa
1 mm Hg = 133.322 Pa
1 lb/in2 = 6894.8 Pa
TemperaturekelvinCelsius
Fahrenheit
1°C = 1 K
1°F = 5/9 K
Volumecubic metrelitre
gallon (U.S.)
gallon (U.K.)
cubic inch
1 L = 1 dm3 = 10-3 m3
1 gal (U.S.) = 3.7854 x 10-3 m3
1 gal (U.K.) = 4.5641 x 10-3 m3
1 in3 = 1.6387 x 10-6 m3

SI Unit Prefixes

FactorsPrefixSymbol
1012teraT
199gigaG
106megaM
103kilok
102hectoh
10-1decid
10-2centic
10-3millim
10-6microµ
10-9nanon
10-12picop
10-15femtof
10-18attoa

# Table of Common Constants

Series of different colored lasers. No matter the color, the speed of light is a constant. The speed of light is just one constant in this table of common constants. Credit: Pang Ka kit, Creative Commons

Here is a useful table of common constants. These physical constants appear time and again in chemistry and physics homework problems.

Why memorize them when you can just look them up.

I personally prefer to keep a sheet with these constants stuffed in the back of book. You can print up your own sheet with a PDF copy of the Table of Common Constants.

### TABLE OF COMMON CONSTANTS

 Name Symbol Value Speed of light c 299792458 m⋅s-1 Charge of an electron e 1.602176565(35)×10−19 C Universal gravitational constant G 6.67384(80)×10-11 N⋅m2/kg2 Planck’s constant h 6.626070040(81)×10−34 J⋅s h 4.135667662(25)×10−15 eV⋅s Dirac’s constant ħ 1.054571800(13)×10−34 J⋅s ħ 6.582119514(40)×10−16 eV⋅s Boltzmann’s constant k 1.3806488(13)×10−23 J⋅K-1 8.6173324(78)×10−5 eV⋅K-1 Avogadro’s constant NA 6.022140857(74)×1023 mol−1 Faraday’s constant F 96485.3365(21) C⋅mol−1 Ideal gas constant R 8.3144621(75) J⋅K−1⋅mol−1 Mass of an electron me 9.10938291(40)×10−31 kg 0.510998928(11) MeV/c2 Mass of a proton mp 1.672621777(74)×10−27 kg 938.272046(21) MeV/c2 Mass of a neutron mn 1.674927351(74)×10−27 kg 939.565378(21) MeV/c2 Atomic mass unit u, amu or Da 1.660538921(73)×10−27 kg 931.494061(21) MeV/c2 Permittivity of free space ε0 8.854187817×10−12 Coulomb’s constant 1/4πε0 8.9875517973681764×109 N⋅m2⋅C-2 Permeability of free space μ0 4π×10−7 N⋅A-2 Rydberg constant R∞ 1.0973731568539(55)×10−7 m-1 Bohr radius a0 5.2917721092(17)×10−11 m