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
Proton vs Atomic nucleus: length comparison
The characteristic size of an atomic nucleus is about 5.95 times the diameter of a proton.
A proton is a positively charged particle found in the nucleus of atoms, made up of quarks.
An atomic nucleus is the compact central part of an atom, made from protons and neutrons.
Both rulers start at the same zero and share one linear scale. Artwork keeps its original proportions.
Measurements, assumptions & sources +
Proton
Diameter: 1.682 fm; measured constant.
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
Characteristic size: 10 fm; representative.
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.
Use the visual comparison to explore its scale, then check the measurements and sources.
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Why this measurement?
Why we use 1.682 fm
We compare the diameter of a proton. This is a measured value; check the notes for its source and scope.
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 measured feature, not the edges of the image. How calibrated comparisons work →
Recorded properties
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
Explore nearby values.
Compare examples with lower, similar and higher values. Each card names the measurement being compared.
Nearest lower valueFundamental physicsPlanck length1.616 × 10⁻³⁵ mLengthThe Planck length is a scale formed from fundamental physical constants.
Nearest higher valueMicroscopic objectsAtomic nucleus10 fmCharacteristic sizeAn atomic nucleus is the compact central part of an atom, made from protons and neutrons.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.