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
Bohr radius vs Hydrogen atom: length comparison
The characteristic size of a hydrogen atom is about 2 times the 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.
A hydrogen atom is the simplest neutral atom, with one proton in its nucleus and one electron around it.
Both rulers start at the same zero and share one linear scale. Artwork keeps its original proportions.
Measurements, assumptions & sources +
Bohr radius
Length: 52.92 pm; measured constant.
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
Characteristic size: 105.8 pm; representative.
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.
Use the visual comparison to explore its scale, then check the measurements and sources.
Change your perspective
Put it next to…
Choose a suggestion to redraw the comparison, or open its page to learn what it is.
Why this measurement?
Why we use 52.92 pm
We compare the Bohr radius. This is a measured value; check the notes for its source and scope.
A characteristic length in a model of hydrogen. It is not the fixed radius of every atom.
The marked horizontal span follows the measured feature, not the edges of the image. How calibrated comparisons work →
Recorded properties
Dimensions and measurements
| Property | Selected value | Recorded range | Basis |
|---|---|---|---|
| 52.92 pm | Not recorded | measured constant |
Around this scale
Explore nearby values.
Compare examples with lower, similar and higher values. Each card names the measurement being compared.
Nearest lower valueFundamental physicsElectron2.426 pmCompton wavelengthAn electron is a fundamental subatomic particle with a negative electric charge, found in atoms and responsible for electricity and chemical bonding.Nearest higher valueMicroscopic objectsHydrogen atom105.8 pmCharacteristic sizeA 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.