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 across
Characteristic size · representative
A little perspective
About twice the length of Bohr radius.
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.
Measurements, assumptions & sources +
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.
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.
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Why this measurement?
Why we use 105.8 pm
For comparison, this page uses characteristic size. This is labelled representative; the central value is useful for comparison, while real values or measurement solutions 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 named feature; transparent margins and unmeasured details do not alter it. How calibrated comparisons work →
Recorded properties
Hydrogen atom 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
Go smaller. Go bigger.
These links use compatible length records, ordered around the selected value.
Nearest lower value · 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.
Nearest higher value · MicroscopicWater molecule280 pmA 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.
Microscopic10 µm cell10 µmA cell is the basic structural unit of living organisms.
People70 µm hair70 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.