Hydrogen atom
A hydrogen atom is the simplest neutral atom, with one proton in its nucleus and one electron around it.
How big is it?
105.8 pm · characteristic size
Characteristic size · representative
A little perspective
Hydrogen atom vs Bohr radius: length comparison
The characteristic size of a hydrogen atom is about 2 times the Bohr radius.
A hydrogen atom is the simplest neutral atom, with one proton in its nucleus and one electron around it.
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.
Both rulers start at the same zero and share one linear scale. Artwork keeps its original proportions.
Measurements, assumptions & sources +
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.
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.
Use the visual comparison to explore its scale, then check the measurements and sources.
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Why this measurement?
Why we use 105.8 pm
We compare the characteristic size of a hydrogen atom. This is a representative comparison value; individual specimens or conditions can vary.
A diameter of twice the Bohr radius, used as a characteristic scale. An electron cloud has no hard outer surface.
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 |
|---|---|---|---|
| 105.8 pm | Not recorded | representative | |
| 1.674 × 10⁻²⁷ kg | Not recorded | representative |
Around this scale
Explore nearby values.
Compare examples with lower, similar and higher values. Each card names the measurement being compared.
Nearest lower valueFundamental physicsBohr radius52.92 pmLengthThe 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.
Nearest higher valueMicroscopic objectsWater molecule280 pmCharacteristic sizeA water molecule is a group of two hydrogen atoms bonded to one oxygen atom.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.
More ways to see it
Curated comparisons
There’s always another scale
Follow your curiosity.
Fundamental physicsProton1.682 fmA proton is a positively charged particle found in the nucleus of atoms, made up of quarks.
MicroscopicCell10 µmA cell is the basic structural unit of living organisms.
PeopleHair70 µmA hair is a slender strand of protein that grows from the skin of humans and other mammals.Fundamental physicsBohr radius52.92 pmThe 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.MicroscopicWater molecule280 pmA water molecule is a group of two hydrogen atoms bonded to one oxygen atom.
MicroscopicGlucose molecule1 nmA glucose molecule is a simple sugar used by living cells as a source of chemical energy.
MicroscopicDNA double helix2 nmDNA is the molecule that stores hereditary information in living organisms.
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.