5.3 a₀ (Bohr radius) is equal to 0.0000000000002804639419668719 km (kilometer). To convert from Bohr radius to kilometer, multiply by 0.000000000000052917724899409786 or divide by 18,897,259,886,000.
physical constant; the most probable distance between an electron and the nucleus in a nonrelativistic model of the hydrogen atom with infinitely heavy nucleus