In 2019, four of the seven SI base units specified in the International System of Quantities were redefined in terms of natural physical constants, rather...

On 20 May 2019, as the final act of the 2019 revision of the SI, the BIPM officially introduced the following new definitions, replacing the preceding...

the same unit. The definition of the dalton was not affected by the 2019 revision of the SI, that is, 1 Da in the SI is still ⁠1/12⁠ of the mass of a...

Austrian scientist Ludwig Boltzmann. As part of the 2019 revision of the SI, the Boltzmann constant is one of the seven "defining constants" that have been...

daltons. With the 2019 revision of the SI, the numerical equivalence is now only approximate but may be assumed for all practical purposes. The mole is widely...

the 2019 revision of the SI, where the kelvin was redefined so that the Boltzmann constant is exactly 1.380649×10−23 J⋅K−1, and the triple point of water...

Since the 2019 revision of the SI, the Faraday constant has an exactly defined value, the product of the elementary charge (e, in coulombs) and the Avogadro...

the 2019 revision of the SI, both NA and k are defined with exact numerical values when expressed in SI units. As a consequence, the SI value of the molar...

quantities in the ratio are masses, the resulting value is dimensionless. These definitions remain valid: 134  even after the 2019 revision of the SI. For a...

of Units (SI).) Because the 2019 revision of the SI gave the Avogadro constant an exact numerical value, the value of the molar mass constant is no longer...

the 2019 revision of the SI, the Josephson constant has an exact value of KJ = 483597.84841698... GHz⋅V−1. The following physical equations use SI units...

(zC). Since the 2019 revision of the SI, the seven SI base units are defined in terms of seven fundamental physical constants, of which the elementary...

(1775–1836), considered the father of electromagnetism along with Danish physicist Hans Christian Ørsted. As of the 2019 revision of the SI, the ampere is defined...

molecular weight when referring to a weighted average of a sample. Prior to the 2019 revision of the SI quantities expressed in daltons (Da) were by definition...

coulombs (symbol C). Under the 2019 revision of the SI, this sets 1 eV equal to the exact value 1.602176634×10−19 J. Historically, the electronvolt was devised...

the new quantity q by:   q s = q 4 π ε 0 . {\displaystyle \ q_{\text{s}}={\frac {q}{\sqrt {4\pi \varepsilon _{0}}}}.} In the 2019 revision of the SI,...

1861. Following the 2019 revision of the SI, in which the ampere and the kilogram were redefined in terms of fundamental constants, the ohm is now also...

joule. If it were still in use, as of the 2019 revision of the SI, its value would be related to the frequency of the electromagnetic radiation by 1 einstein...

scale using this definition. The 2019 revision of the SI now defines the kelvin in terms of energy by setting the Boltzmann constant to exactly 1.380649×10−23 joules...

⁠1/299792458⁠ of a second. After the 2019 revision of the SI, this definition was rephrased to include the definition of a second in terms of the caesium frequency...

It can be also expressed in terms of SI derived units, N⋅A−2. Since the revision of the SI in 2019 (when the values of e and h were fixed as defined quantities)...

the International Prototype of the Kilogram and the International Prototype Metre, although both have been superseded during the 2019 revision of the...

compared to the empty space between them. One mole of an ideal gas has a volume of 22.71095464... L (exact value based on 2019 revision of the SI) at standard...

constant NA before its value was fixed as a defining constant in the 2019 revision of the SI: N A = M u A r ( e ) m e = M u A r ( e ) c α 2 2 R ∞ h . {\displaystyle...

according to his model of the atom. Before the 2019 revision of the SI, R ∞ {\displaystyle R_{\infty }} and the electron spin g-factor were the most accurately...

used for the purpose of defining the volt. As a consequence of the 2019 revision of the SI, as of 2019 the Josephson constant has an exact value of KJ = 483597...

historical and practical reasons. See 2019 revision of the SI. A set of base dimensions of quantity is a minimal set of units such that every physical quantity...

subsystems. The CGS-to-SI correspondence of electromagnetic units as given was exact prior to the 2019 revision of the SI, until which the magnetic constant...

kelvin in terms of invariant constants of physics, ultimately resulting in the 2019 revision of the SI, which finally eliminated the need for any physical...

that of the kilogram. From 1954 to 2019, the SI temperature scales were defined using the triple point of water and absolute zero. The 2019 revision replaced...