bohr

https://doi.org/10.1351/goldbook.B00691
Atomic unit of length, \[a_{0}\approx 5.291\ 772\ 49(24)\times 10^{-11}\ \text{m}\]
Source:
Green Book, 2nd ed., p. 76 (https://dev.goldbook.iupac.org/files/pdf/green_book_2ed.pdf)