Physical Constants

Look up and copy 80 physical and chemical constants, such as the speed of light, the Planck constant, the Avogadro constant and the gas constant, as CODATA 2022 recommended values. Use it to check a value, its unit and its uncertainty for homework or lab calculations.

How to use

1. Type a name or symbol into "Find" (for example Planck, h, k), or choose a group under "Category", such as "The 7 SI defining constants", "Universal" or "Electromagnetic".
2. Switch "Units" between SI and "eV units". eV values exist only for constants that NIST also lists in eV-based units.
3. Choose "Number only", "Scientific" or "With unit" under "Copy as", then press "Copy" next to a constant.

How it works

• Values are the CODATA 2022 recommended values published by NIST, with the digits copied exactly. Digits in brackets are the standard uncertainty in the last digits: 6.674 30(15) means 6.674 30 ± 0.000 15.
• Constants marked "SI defining" or "Exact" have no uncertainty. A value ending in … is exact but cut off at the digits shown.
• The astronomical unit, parsec and nominal solar and Earth values follow IAU resolutions, and the standard-state pressure (1 bar) is the IUPAC definition.

Questions and answers

What is the exact value of Avogadro's number?

6.022 140 76 × 10²³ mol⁻¹. Since the 2019 redefinition of the SI it is a defined value with no uncertainty.

What is the value of the gas constant R?

8.314 462 618… J mol⁻¹ K⁻¹. It is the product of the Avogadro and Boltzmann constants, so it is exact; the page shows it cut off at the digits given.

Why does the gravitational constant G have an uncertainty?

G is measured, not defined. The CODATA 2022 value is 6.674 30(15) × 10⁻¹¹ m³ kg⁻¹ s⁻².

Are standard gravity and the standard atmosphere included?

Yes. "Astronomical, Earth and conventional" lists standard gravity as 9.806 65 m s⁻² and the standard atmosphere as 101 325 Pa, both exact.