Convert Mil to Fathom
Convert mils to fathoms instantly. 1 mil = 1.388889e-5 fathom — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Fathom to Mil converter for the reverse conversion.
Units explained
Mil
A mil (also called a thou) is an Imperial unit of length equal to one thousandth of an inch (1/1000 in = 0.0254 mm = 25.4 μm exactly). It is used in engineering, manufacturing, and materials specifications.
The mil is derived from the Latin mille, "thousand," denoting one-thousandth of an inch. Standardized in industrial use during the 19th-century rise of precision engineering.
Mils are used to specify thicknesses of plastic films, foils, paper, copper traces on printed circuit boards (PCBs), wire insulation, and paint coatings. A standard sheet of paper is about 4 mils thick.
Adopted in 19th-century engineering practice; the value (1/1000 in) became exact in 1959 when the inch was fixed at 25.4 mm via the International Yard and Pound Agreement. The British term is "thou"; American term is "mil".
Fathom
A fathom is an Imperial unit of length equal to 6 feet or exactly 1.8288 meters. It is used almost exclusively for measuring water depth in maritime contexts.
The fathom derives from the Old English word fæthm, meaning "the embracing arms" — the distance between the fingertips of a person's outstretched arms. Standardized at 6 feet in English maritime tradition.
Fathoms are used in nautical depth charts, scuba diving, oceanography, and maritime literature. Despite metrication efforts, fathoms remain common in English-language nautical charts and recreational diving.
Old English origin (predating 1066); standardized at 6 feet by English maritime tradition; fixed at 1.8288 m exactly via the 1959 International Yard and Pound Agreement.
Mil to Fathom conversion formula
The relationship between mils and fathoms:
To convert mils to fathoms, multiply the value in mils by 1.388889e-5. To reverse, multiply fathoms by 72000.
How to use this converter
Type a value into the calculator. The result in fathoms updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Fathom to Mil converter for the reverse direction.
Step-by-step: convert mils to fathoms
- Write down the value in mils (mil).
- Multiply that value by the factor 1.388889e-5.
- The product is the equivalent value in fathoms (ftm).
- To reverse, multiply the fathom value by 72000.
Worked examples
Example 1 — Convert 1 mil to ftm:
1 × 1.388889e-5 = 1.388889e-5 ftm
Example 2 — Convert 100 mil to ftm:
100 × 1.388889e-5 = 0.0013888889 ftm
Real-world example — Macro-scale buildup
A million mils equals exactly one fathom — the conversion that bridges microscale features and macroscale objects in microfluidic, biomedical, and semiconductor packaging design.
1000000 mil × 1.388889e-5 = 13.8888888889 ftm
Real-world example — Quarter-meter measurement reference
A 250,000-mil length equals 0.25 fathoms — useful for comparing supply-chain spec sheets where some lengths are quoted in the smaller unit and some in the larger.
250000 mil × 1.388889e-5 = 3.4722222222 ftm
Real-world example — From microscopic to macroscopic
A million mils equals exactly one fathom. This kind of conversion appears in microfluidics, where total channel length is given in fathoms but feature widths are in mils.
1000000 mil × 1.388889e-5 = 13.8888888889 ftm
Mil to Fathom conversion table
Standard reference values for converting mils to fathoms:
| Mil [mil] | Fathom [ftm] |
|---|---|
| 0.01 | 1.388889e-7 |
| 0.1 | 1.388889e-6 |
| 1 | 1.388889e-5 |
| 2 | 2.777778e-5 |
| 3 | 4.166667e-5 |
| 4 | 5.555556e-5 |
| 5 | 6.944444e-5 |
| 10 | 0.0001388889 |
| 20 | 0.0002777778 |
| 30 | 0.0004166667 |
| 40 | 0.0005555556 |
| 50 | 0.0006944444 |
| 100 | 0.0013888889 |
| 500 | 0.0069444444 |
| 1000 | 0.0138888889 |
Frequently asked questions
How many fathoms is 1 mil?
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How many fathoms is 100 mils?
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Metric / SI (7 units)
Imperial / US Customary (26 units)
Nautical (1 units)
Sources & references
Conversion factor (1 mil = 1.388889e-5 ftm) 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.