Convert Femtometer to Megameter
Convert femtometers to megameters instantly. 1 femtometer = 1e-21 megameter — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Megameter to Femtometer converter for the reverse conversion.
Units explained
Femtometer
A femtometer is a metric unit of length equal to one quadrillionth of a meter (1×10⁻¹⁵ m). It is the standard unit for measuring sub-atomic dimensions, particularly the size of atomic nuclei. The femtometer is also known historically as the fermi.
The femtometer was defined using the SI prefix femto- (from Danish femten, meaning fifteen), adopted by the CGPM in 1964 to denote one quadrillionth. The synonymous name fermi was named after Italian physicist Enrico Fermi.
Femtometers are used to express the size of atomic nuclei (typically 1–10 fm in diameter), the range of strong nuclear forces, and characteristic dimensions in particle physics. The proton charge radius is approximately 0.84 fm.
SI prefix femto- adopted in 1964; the unit became standard in nuclear physics through the late 20th century. The name fermi (after Enrico Fermi) was used informally from the 1950s but officially superseded by femtometer.
Megameter
A megameter is a metric unit of length equal to one million meters (1×10⁶ m, or 1,000 km). It is occasionally used in geophysics and astronomy when expressing planetary-scale distances in SI units.
The megameter uses the SI prefix mega- (from Greek megas, great), adopted by the CGPM in 1960 to denote multiplication by one million.
Megameters appear in geophysics (Earth's mean radius is 6.371 Mm), planetary science, and large-scale civil engineering planning. The unit is less common than the kilometer for everyday geographic distances.
SI prefix mega- adopted in 1960; the megameter is the standard SI prefix unit for distances comparable to planetary radii.
Femtometer to Megameter conversion formula
The relationship between femtometers and megameters:
To convert femtometers to megameters, multiply the value in femtometers by 1e-21. To reverse, multiply megameters by 1e+21.
How to use this converter
Type a value into the calculator. The result in megameters updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Megameter to Femtometer converter for the reverse direction.
Step-by-step: convert femtometers to megameters
- Write down the value in femtometers (fm).
- Multiply that value by the factor 1e-21.
- The product is the equivalent value in megameters (Mm).
- To reverse, multiply the megameter value by 1e+21.
Worked examples
Example 1 — Convert 1 fm to Mm:
1 × 1e-21 = 1e-21 Mm
Example 2 — Convert 100 fm to Mm:
100 × 1e-21 = 1e-19 Mm
Real-world example — Molecular dimensions
The diameter of small molecular structures (around 2 femtometers) is often converted into related sub-micron units when comparing measurements across different microscopy techniques or imaging modalities.
2 fm × 1e-21 = 2e-21 Mm
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 femtometers can be re-expressed in megameters for direct comparison with another instrument's calibration data sheet.
800 fm × 1e-21 = 8e-19 Mm
Femtometer to Megameter conversion table
Standard reference values for converting femtometers to megameters:
| Femtometer [fm] | Megameter [Mm] |
|---|---|
| 0.01 | 1e-23 |
| 0.1 | 1e-22 |
| 1 | 1e-21 |
| 2 | 2e-21 |
| 3 | 3e-21 |
| 4 | 4e-21 |
| 5 | 5e-21 |
| 10 | 1e-20 |
| 20 | 2e-20 |
| 30 | 3e-20 |
| 40 | 4e-20 |
| 50 | 5e-20 |
| 100 | 1e-19 |
| 500 | 5e-19 |
| 1000 | 1e-18 |
Frequently asked questions
How many megameters is 1 femtometer?
How do I convert femtometers to megameters?
How do I convert megameters back to femtometers?
How many megameters is 100 femtometers?
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Metric / SI (17 units)
Imperial / US Customary (4 units)
Sources & references
Conversion factor (1 fm = 1e-21 Mm) 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 Astronomical Union — System of Astronomical Constants
The IAU defines astronomical units including the AU (149597870700 m exactly) light-year and parsec used in astronomy and astrophysics.