ConstantID

Adopted values

Values fixed by agreement rather than measured: the seven SI defining constants and conventions such as standard gravity and the standard atmosphere.

Physico-chemical exact NA Avogadro constant 6.022 140 76 × 1023 mol−1 Physico-chemical exact k Boltzmann constant 1.380 649 × 10−23 J K−1 Electromagnetic exact e Elementary charge 1.602 176 634 × 10−19 C Adopted exact ΔνCs Caesium frequency 9 192 631 770 Hz Adopted exact Kcd Luminous efficacy 683 lm W−1 Universal exact h Planck constant 6.626 070 15 × 10−34 J Hz−1 Universal exact ℏ Reduced Planck constant 1.054 571 817… × 10−34 J s Universal exact c Speed of light 299 792 458 m s−1 Adopted exact gn Standard gravity 9.806 65 m s−2

All 11 values

SymbolQuantityValue (uncertainty)UnitRel. unc.
NA Avogadro constant 6.022 140 76 × 1023 mol−1 exact
k Boltzmann constant 1.380 649 × 10−23 J K−1 exact
e Elementary charge 1.602 176 634 × 10−19 C exact
ΔνCs Hyperfine transition frequency of Cs-133 9 192 631 770 Hz exact
Kcd Luminous efficacy 683 lm W−1 exact
h Planck constant 6.626 070 15 × 10−34 J Hz−1 exact
ℏ Reduced Planck constant 1.054 571 817… × 10−34 J s exact
c Speed of light in vacuum 299 792 458 m s−1 exact
gn Standard acceleration of gravity 9.806 65 m s−2 exact
atm Standard atmosphere 101 325 Pa exact
p∘ Standard-state pressure 100 000 Pa exact