Convert Classical Electron Radius to Fermi
Convert classical electron radii to fermis instantly. 1 classical electron radius = 2.8179403262 fermi — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Fermi to Classical Electron Radius converter for the reverse conversion.
Units explained
Classical Electron Radius
The classical electron radius is approximately 2.818×10⁻¹⁵ meters. It is the radius an electron would have if its mass were entirely electromagnetic and its charge distributed over its surface.
Defined classically in the early 20th century. The CODATA 2018 value of 2.8179403262×10⁻¹⁵ m is derived from the elementary charge, electron rest mass, and the Coulomb constant.
The classical electron radius appears in scattering theory (Thomson scattering cross-section), particle physics estimates, and historical electromagnetism. It is a calculational tool, not the actual size of an electron, which has no measured extent.
Concept dates to the early 20th-century classical electromagnetism; CODATA 2018 provides the current reference value.
Fermi
A fermi is a unit of length equal to one femtometer (1×10⁻¹⁵ m). It is named after physicist Enrico Fermi and is widely used in nuclear physics as a synonym for the femtometer.
The fermi was introduced informally in mid-20th-century nuclear physics literature. Although the BIPM has formally standardised the SI name 'femtometer', the fermi remains in widespread informal use.
Fermis are used to express nuclear sizes, hadron radii, and characteristic length scales in particle physics. Functionally identical to the femtometer.
Named after Enrico Fermi; in informal use from the 1950s; officially equivalent to the SI femtometer.
Classical Electron Radius to Fermi conversion formula
The relationship between classical electron radii and fermis:
To convert classical electron radii to fermis, multiply the value in classical electron radii by 2.8179403262. To reverse, multiply fermis by 0.3548691187.
How to use this converter
Type a value into the calculator. The result in fermis updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Fermi to Classical Electron Radius converter for the reverse direction.
Step-by-step: convert classical electron radii to fermis
- Write down the value in classical electron radii (rₑ).
- Multiply that value by the factor 2.8179403262.
- The product is the equivalent value in fermis (F).
- To reverse, multiply the fermi value by 0.3548691187.
Worked examples
Example 1 — Convert 1 rₑ to F:
1 × 2.8179403262 = 2.8179403262 F
Example 2 — Convert 100 rₑ to F:
100 × 2.8179403262 = 281.79403262 F
Real-world example — Wavelengths across the spectrum
Optical and atomic-scale phenomena are routinely cross-converted between sub-micron units. A photon of wavelength 800 classical electron radii can be re-expressed in fermis for direct comparison with another instrument's calibration data sheet.
800 rₑ × 2.8179403262 = 2254.35226096 F
Real-world example — Molecular dimensions
The diameter of small molecular structures (around 2 classical electron radii) is often converted into related sub-micron units when comparing measurements across different microscopy techniques or imaging modalities.
2 rₑ × 2.8179403262 = 5.6358806524 F
Classical Electron Radius to Fermi conversion table
Standard reference values for converting classical electron radii to fermis:
| Classical Electron Radius [rₑ] | Fermi [F] |
|---|---|
| 0.01 | 0.0281794033 |
| 0.1 | 0.2817940326 |
| 1 | 2.8179403262 |
| 2 | 5.6358806524 |
| 3 | 8.4538209786 |
| 4 | 11.2717613048 |
| 5 | 14.089701631 |
| 10 | 28.179403262 |
| 20 | 56.358806524 |
| 30 | 84.538209786 |
| 40 | 112.717613048 |
| 50 | 140.89701631 |
| 100 | 281.79403262 |
| 500 | 1408.9701631 |
| 1000 | 2817.9403262 |
Frequently asked questions
How many fermis is 1 classical electron radius?
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How many fermis is 100 classical electron radii?
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Sources & references
Conversion factor (1 rₑ = 2.8179403262 F) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- NIST — Refinement of values for the yard and pound (Federal Register 1959)
The treaty (signed by US
- International Hydrographic Organization — Resolution on the Nautical Mile
International authority that standardised the nautical mile at exactly 1852 m in 1929 — the value adopted worldwide for sea and air navigation.