Proton
A proton is a positively charged particle found in the nucleus of atoms, made up of quarks.
How big is it?
1.682 fm across
Diameter · measured constant
A little perspective
Atomic nucleus is about 5.95 times larger on this measurement.
Atomic nucleus: An atomic nucleus is the compact central part of an atom, made from protons and neutrons.
Measurements, assumptions & sources +
Proton
Twice the approximately 0.8409 fm charge radius. The charge distribution has no hard boundary; the illustration is schematic.
NIST — 2022 CODATA fundamental constants
The marked diameter is calibrated. Unmeasured illustration details are representative.
Atomic nucleus
A 10 fm diameter scale model of a heavy nucleus. Nuclear size depends on the number of nucleons.
University of Utah — Cell size and scale
The marked characteristic size is calibrated. Unmeasured illustration details are representative.
Change your perspective
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Why this measurement?
Why we use 1.682 fm
For comparison, this page uses diameter. This is labelled measured constant; the central value is useful for comparison, while real values or measurement solutions can vary.
Twice the approximately 0.8409 fm charge radius. The charge distribution has no hard boundary; the illustration is schematic.
The marked horizontal span follows the named feature; transparent margins and unmeasured details do not alter it. How calibrated comparisons work →
Recorded properties
Proton dimensions and measurements
| Property | Selected value | Recorded range | Basis |
|---|---|---|---|
| 1.682 fm | Not recorded | measured constant | |
| 1.673 × 10⁻²⁷ kg | Not recorded | measured constant |
Around this scale
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These links use compatible length records, ordered around the selected value.
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 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.
MicroscopicAtomic nucleus10 fmAn atomic nucleus is the compact central part of an atom, made from protons and neutrons.
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.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.