Planck length
The Planck length is a scale formed from fundamental physical constants. It marks a regime where present theories of gravity and quantum physics are expected to need a unified description.
Also known as: planck, planck scale
How big is it?
1.616 × 10⁻³⁵ m long
Length · theoretical
A little perspective
Proton is about 1.04 × 10²⁰ times larger on this measurement.
Proton: A proton is a positively charged particle found in the nucleus of atoms, made up of quarks.
Measurements, assumptions & sources +
Planck length
A theoretical scale formed from the speed of light, reduced Planck constant and gravitational constant. It is not experimentally established as the smallest possible length. The area and volume are derived mathematical scales.
NIST — 2022 CODATA fundamental constants
The marked length is calibrated. Unmeasured illustration details are representative.
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.
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Why this measurement?
Why we use 1.616 × 10⁻³⁵ m
For comparison, this page uses length. This is a theoretical scale, not a measured hard boundary or proof of a physical limit.
A theoretical scale formed from the speed of light, reduced Planck constant and gravitational constant. It is not experimentally established as the smallest possible length. The area and volume are derived mathematical scales.
The marked horizontal span follows the named feature; transparent margins and unmeasured details do not alter it. How calibrated comparisons work →
Recorded properties
Planck length dimensions and measurements
| Property | Selected value | Recorded range | Basis |
|---|---|---|---|
| 1.616 × 10⁻³⁵ m | Not recorded | theoretical | |
| 2.612 × 10⁻⁷⁰ m² | Not recorded | theoretical | |
| 4.222 × 10⁻¹⁰² L | Not recorded | theoretical | |
| 5.391 × 10⁻⁴⁴ s | Not recorded | theoretical |
Around this scale
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Sources and method
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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.
MicroscopicHydrogen atom105.8 pmA hydrogen atom is the simplest neutral atom, with one proton in its nucleus and one electron around it.
SpaceObservable universe28.21 GpcThe observable universe is the region from which light or other signals have had time to reach us since the early universe.Fundamental physicsPlanck mass21.76 µgThe Planck mass is a theoretical mass scale derived from fundamental constants, significant in discussions of quantum gravity.
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.