Convert Fermi to Classical Electron Radius
Convert fermis to classical electron radii instantly. 1 fermi = 0.3548691187 classical electron radius — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Classical Electron Radius to Fermi converter for the reverse conversion.
Units explained
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
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 to Classical Electron Radius conversion formula
The relationship between fermis and classical electron radii:
To convert fermis to classical electron radii, multiply the value in fermis by 0.3548691187. To reverse, multiply classical electron radii by 2.8179403262.
How to use this converter
Type a value into the calculator. The result in classical electron radii updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Classical Electron Radius to Fermi converter for the reverse direction.
Step-by-step: convert fermis to classical electron radii
- Write down the value in fermis (F).
- Multiply that value by the factor 0.3548691187.
- The product is the equivalent value in classical electron radii (rₑ).
- To reverse, multiply the classical electron radius value by 2.8179403262.
Worked examples
Example 1 — Convert 1 F to rₑ:
1 × 0.3548691187 = 0.3548691187 rₑ
Example 2 — Convert 100 F to rₑ:
100 × 0.3548691187 = 35.4869118662 rₑ
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 fermis can be re-expressed in classical electron radii for direct comparison with another instrument's calibration data sheet.
800 F × 0.3548691187 = 283.8952949294 rₑ
Real-world example — Molecular dimensions
The diameter of small molecular structures (around 2 fermis) is often converted into related sub-micron units when comparing measurements across different microscopy techniques or imaging modalities.
2 F × 0.3548691187 = 0.7097382373 rₑ
Fermi to Classical Electron Radius conversion table
Standard reference values for converting fermis to classical electron radii:
| Fermi [F] | Classical Electron Radius [rₑ] |
|---|---|
| 0.01 | 0.0035486912 |
| 0.1 | 0.0354869119 |
| 1 | 0.3548691187 |
| 2 | 0.7097382373 |
| 3 | 1.064607356 |
| 4 | 1.4194764746 |
| 5 | 1.7743455933 |
| 10 | 3.5486911866 |
| 20 | 7.0973823732 |
| 30 | 10.6460735599 |
| 40 | 14.1947647465 |
| 50 | 17.7434559331 |
| 100 | 35.4869118662 |
| 500 | 177.4345593309 |
| 1000 | 354.8691186618 |
Frequently asked questions
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Sources & references
Conversion factor (1 F = 0.3548691187 rₑ) 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.