Bohr radius
The Bohr radius is a fundamental physical constant representing the most probable distance between the nucleus and the electron in a hydrogen atom according to early quantum theory.
How big is it?
52.92 pm long
Length · measured constant
A little perspective
Hydrogen atom is about 2 times larger on this measurement.
Hydrogen atom: A hydrogen atom is the simplest neutral atom, with one proton in its nucleus and one electron around it.
Measurements, assumptions & sources +
Bohr radius
A characteristic length in a model of hydrogen. It is not the fixed radius of every atom.
NIST — 2022 CODATA fundamental constants
The marked length is calibrated. Unmeasured illustration details are representative.
Hydrogen atom
A diameter of twice the Bohr radius, used as a characteristic scale. An electron cloud has no hard outer surface.
NIST — 2022 CODATA fundamental constants
The marked characteristic size is calibrated. Unmeasured illustration details are representative.
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Why this measurement?
Why we use 52.92 pm
For comparison, this page uses length. This is labelled measured constant; the central value is useful for comparison, while real values or measurement solutions can vary.
A characteristic length in a model of hydrogen. It is not the fixed radius of every atom.
The marked horizontal span follows the named feature; transparent margins and unmeasured details do not alter it. How calibrated comparisons work →
Recorded properties
Bohr radius dimensions and measurements
| Property | Selected value | Recorded range | Basis |
|---|---|---|---|
| 52.92 pm | Not recorded | measured constant |
Around this scale
Go smaller. Go bigger.
These links use compatible length records, ordered around the selected value.
Nearest lower value · Fundamental physicsElectron2.426 pmAn electron is a fundamental subatomic particle with a negative electric charge, found in atoms and responsible for electricity and chemical bonding.Nearest higher value · MicroscopicHydrogen atom105.8 pmA hydrogen atom is the simplest neutral atom, with one proton in its nucleus and one electron around it.Sources and method
Want to check the number?
The source records and measurement method remain available for inspection.
- NIST — 2022 CODATA fundamental constantsRecommended constants with uncertainties; exact SI definitions are distinguished from measured constants.
There’s always another scale
Follow your curiosity.
Fundamental physicsPlanck length1.616 × 10⁻³⁵ mThe Planck length is a scale formed from fundamental physical constants.MicroscopicHydrogen atom105.8 pmA hydrogen atom is the simplest neutral atom, with one proton in its nucleus and one electron around it.
MicroscopicDNA double helix2 nmDNA is the molecule that stores hereditary information in living organisms.
MicroscopicWater molecule280 pmA water molecule is a group of two hydrogen atoms bonded to one oxygen atom.Fundamental physicsElectron9.109 × 10⁻³¹ kgAn electron is a fundamental subatomic particle with a negative electric charge, found in atoms and responsible for electricity and chemical bonding.
MicroscopicGlucose molecule1 nmA glucose molecule is a simple sugar used by living cells as a source of chemical energy.
MicroscopicIgG antibody molecule14.5 nmAn IgG antibody molecule is a Y-shaped protein produced by the immune system to identify and neutralise foreign substances.
MicroscopicRibosome25 nmA ribosome is a molecular machine that builds proteins by reading instructions carried by messenger RNA.