Units and Constants

CODATA 2018 values in SI and CGS, copied with a click, and a unit converter with NIST factors. A constant that has a card in the formula sheet leads to the problems it is needed in.

Physical constants

CODATA 2018 recommended values (NIST SP 961). Click a row to copy the value.

Name	Symbol	Value
Universal
Speed of light in vacuum	$$c$$	299 792 458m/s2.997 924 58 × 10¹⁰cm/s	in problems
Planck constant	$$h$$	6.626 070 15 × 10⁻³⁴J·s6.626 070 15 × 10⁻²⁷erg·s	in problems
Reduced Planck constant	$\hbar$	1.054 571 817 × 10⁻³⁴J·s1.054 571 817 × 10⁻²⁷erg·s
Gravitational constant	$$G$$	6.674 30 × 10⁻¹¹N·m²/kg²6.674 30 × 10⁻⁸cm³/(g·s²)± 2.2 × 10⁻⁵	in problems
Boltzmann constant	$$k_B$$	1.380 649 × 10⁻²³J/K1.380 649 × 10⁻¹⁶erg/K	in problems
Stefan-Boltzmann constant	$\sigma$	5.670 374 419 × 10⁻⁸W/(m²·K⁴)5.670 374 419 × 10⁻⁵erg/(s·cm²·K⁴)	in problems
Speed of sound in air (20°C)		~343m/s~3.43 × 10⁴cm/s
Electromagnetic
Elementary charge	$$e$$	1.602 176 634 × 10⁻¹⁹C4.803 204 71 × 10⁻¹⁰statC (esu)
Vacuum permittivity	$\varepsilon_0$	8.854 187 8128 × 10⁻¹²F/m1 (dimensionless)	in problems
Vacuum permeability	$\mu_0$	1.256 637 062 12 × 10⁻⁶N/A²1 (dimensionless)	in problems
Coulomb constant	$$k_e$$	8.987 551 7923 × 10⁹N·m²/C²1 (dimensionless)	in problems
Magnetic flux quantum	$\Phi_0$	2.067 833 848 × 10⁻¹⁵Wb2.067 833 848 × 10⁻⁷Mx
Conductance quantum	$$G_0$$	7.748 091 729 × 10⁻⁵S7.748 091 729 × 10⁻⁵S
Fine-structure constant	$\alpha$	7.297 352 5693 × 10⁻³(dimensionless)7.297 352 5693 × 10⁻³(dimensionless)± 1.5 × 10⁻¹⁰
Impedance of free space	$$Z_0$$	376.730 313 668 $\Omega$ 376.730 313 668 $\Omega$
Atomic and nuclear
Electron mass	$$m_e$$	9.109 383 7015 × 10⁻³¹kg9.109 383 7015 × 10⁻²⁸g± 3.0 × 10⁻¹⁰
Proton mass	$$m_p$$	1.672 621 923 69 × 10⁻²⁷kg1.672 621 923 69 × 10⁻²⁴g± 3.1 × 10⁻¹⁰
Neutron mass	$$m_n$$	1.674 927 498 04 × 10⁻²⁷kg1.674 927 498 04 × 10⁻²⁴g± 5.7 × 10⁻¹⁰
Atomic mass unit	$$u$$	1.660 539 066 60 × 10⁻²⁷kg1.660 539 066 60 × 10⁻²⁴g± 3.0 × 10⁻¹⁰
Bohr radius	$$a_0$$	5.291 772 109 03 × 10⁻¹¹m5.291 772 109 03 × 10⁻⁹cm± 1.5 × 10⁻¹⁰
Classical electron radius	$$r_e$$	2.817 940 3262 × 10⁻¹⁵m2.817 940 3262 × 10⁻¹³cm± 4.5 × 10⁻¹⁰	in problems
Rydberg constant	$R_\infty$	10 973 731.568 160m⁻¹109 737.315 681 60cm⁻¹± 1.9 × 10⁻¹²
Bohr magneton	$\mu_B$	9.274 010 0783 × 10⁻²⁴J/T9.274 010 0783 × 10⁻²¹erg/G± 3.0 × 10⁻¹⁰
Nuclear magneton	$\mu_N$	5.050 783 7461 × 10⁻²⁷J/T5.050 783 7461 × 10⁻²⁴erg/G± 3.1 × 10⁻¹⁰
Electron g-factor	$$g_e$$	-2.002 319 304 362 56(dimensionless)-2.002 319 304 362 56(dimensionless)± 3.5 × 10⁻¹³
Proton-electron mass ratio	$$m_p/m_e$$	1836.152 673 43(dimensionless)1836.152 673 43(dimensionless)± 6.0 × 10⁻¹¹
Compton wavelength	$\lambda_C$	2.426 310 238 67 × 10⁻¹²m2.426 310 238 67 × 10⁻¹⁰cm± 3.0 × 10⁻¹⁰
Thermodynamic
Avogadro constant	$$N_A$$	6.022 140 76 × 10²³mol⁻¹6.022 140 76 × 10²³mol⁻¹	in problems
Gas constant	$$R$$	8.314 462 618J/(mol·K)8.314 462 618 × 10⁷erg/(mol·K)	in problems
Faraday constant	$$F$$	96 485.332 12C/mol96 485.332 12C/mol
Molar Planck constant	$$N_A h$$	3.990 312 712 × 10⁻¹⁰J·s/mol3.990 312 712 × 10⁻³erg·s/mol
First radiation constant	$$c_1$$	3.741 771 852 × 10⁻¹⁶W·m²3.741 771 852 × 10⁻⁵erg·cm²/s
Second radiation constant	$$c_2$$	1.438 776 877 × 10⁻²m·K1.438 776 877cm·K
Wien displacement constant	$$b$$	2.897 771 955 × 10⁻³m·K0.289 777 1955cm·K
Loschmidt constant	$$n_0$$	2.686 7774 × 10²⁵m⁻³2.686 7774 × 10¹⁹cm⁻³
Molar volume (ideal gas, STP)	$$V_m$$	22.413 969 54 × 10⁻³m³/mol22 413.969 54cm³/mol
Other
Standard gravity	$$g$$	9.806 65m/s²980.665cm/s²	in problems
Standard atmosphere	$\text{atm}$	101 325Pa1 013 250dyn/cm²
Electron volt	$\text{eV}$	1.602 176 634 × 10⁻¹⁹J1.602 176 634 × 10⁻¹²erg
Thomson cross section	$\sigma_T$	6.652 458 7321 × 10⁻²⁹m²6.652 458 7321 × 10⁻²⁵cm²± 9.1 × 10⁻¹⁰
Hartree energy	$$E_h$$	4.359 744 722 2071 × 10⁻¹⁸J4.359 744 722 2071 × 10⁻¹¹erg± 3.0 × 10⁻¹⁰
Josephson constant	$$K_J$$	483 597.8484 × 10⁹Hz/V483 597.8484 × 10⁹Hz/V
von Klitzing constant	$$R_K$$	25 812.807 45 $\Omega$ 25 812.807 45 $\Omega$

No constant matches.

Unit converter

Conversion between SI, CGS and other systems. Factors from NIST/CODATA recommended values.

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