1 femtometre
1 fmLength · definition
The quantity is exact as entered. Comparisons use the clearly stated specimen, model or nominal measurement.
Length & distance
Just how long is 1 femtometre?
Microscopic
1 fm
1 × 10⁻¹⁵ mmetres
3.2808 × 10⁻¹⁵ ftfeet
6.2137 × 10⁻¹⁹ mimiles
6.6846 × 10⁻²⁷ AUastronomical units
01
1 femtometre1 fmLength · definition
02
Proton1.682 fmDiameter · measured constant
Both marked spans share one linear scale. Artwork keeps its proportions; poses and surface detail are illustrative.
A little perspective
The diameter of Proton is about 1.68 times the length of 1 femtometre.
Measurements, assumptions & sources +
1 femtometre
The quantity is exact as entered. Comparisons use the clearly stated specimen, model or nominal measurement.
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.
Measurement details
Why these numbers?
The visual compares length with diameter. The records below preserve each value’s basis and caveats.
Proton
1.682 fmDiameter · measured constant
Twice the approximately 0.8409 fm charge radius. The charge distribution has no hard boundary; the illustration is schematic.
- Comparing
- Length ↔ Diameter
- Relative size
- Proton is larger on this measurement by a factor of about 1.68. Proton's selected measurement is approximately 68.2% greater than 1 femtometre's.
How to read the visual
The labelled spans and stored measurements determine the scale; unmeasured illustration details do not.
- Proton is labelled measured constant; treat the displayed value as a comparison anchor rather than false precision.
Change your perspective
Put it next to…
Choose a suggestion to redraw the comparison, or open its page to learn what it is.
A little smaller. A little larger.