Fathom to Arpent Converter
Convert fathoms to arpents with our free online length converter.
Quick Answer
1 Fathom = 0.031277 arpents
Formula: Fathom × conversion factor = Arpent
Use the calculator below for instant, accurate conversions.
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Fathom to Arpent Calculator
How to Use the Fathom to Arpent Calculator:
- Enter the value you want to convert in the 'From' field (Fathom).
- The converted value in Arpent will appear automatically in the 'To' field.
- Use the dropdown menus to select different units within the Length category.
- Click the swap button (⇌) to reverse the conversion direction.
How to Convert Fathom to Arpent: Step-by-Step Guide
Converting Fathom to Arpent involves multiplying the value by a specific conversion factor, as shown in the formula below.
Formula:
1 Fathom = 0.031277 arpentsExample Calculation:
Convert 10 fathoms: 10 × 0.031277 = 0.31277 arpents
Disclaimer: For Reference Only
These conversion results are provided for informational purposes only. While we strive for accuracy, we make no guarantees regarding the precision of these results, especially for conversions involving extremely large or small numbers which may be subject to the inherent limitations of standard computer floating-point arithmetic.
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Need to convert to other length units?
View all Length conversions →What is a Fathom and a Arpent?
The Six-Foot Maritime Standard
The fathom is defined as exactly 6 feet in the imperial and U.S. customary measurement systems.
Precise equivalents:
- 6 feet (by definition)
- 2 yards (6 ft ÷ 3 ft/yd)
- 72 inches (6 ft × 12 in/ft)
- 1.8288 meters (exactly, using 1 ft = 0.3048 m)
- 182.88 centimeters
Historical basis: The arm span of an average man with arms fully outstretched, measured from fingertip to fingertip.
Arm Span Origins
Old English "fæthm":
- Primary meaning: To embrace, encircle with outstretched arms
- Secondary meaning: The distance between fingertips when arms are extended
Practical measurement: Sailors hauling in sounding lines (weighted ropes for measuring depth) would pull hand-over-hand, with each arm span representing one fathom. This created a natural counting method:
- Drop weighted line overboard
- Haul in, counting arm spans
- Number of arm spans = depth in fathoms
Standardization necessity: Since arm spans varied (5.5-6.5 feet typically), maritime commerce required a fixed standard. The British settled on exactly 6 feet, matching the standardized foot of 12 inches.
Nautical Charts and Depth Contours
Fathom lines: Nautical charts show depth contours (lines connecting points of equal depth) traditionally measured in fathoms.
Common contour intervals:
- 1, 2, 3, 5, 10 fathoms: Shallow coastal waters
- 20, 50, 100 fathoms: Coastal navigation
- 500, 1,000 fathoms: Deep ocean
Chart notation: Depths written as plain numbers on charts (e.g., "45") indicate 45 fathoms unless otherwise specified. Modern charts often include a note: "Depths in fathoms" or "Depths in meters."
Anchor Cable and Chain
Shackle: One "shackle" of anchor chain traditionally equals 15 fathoms (90 feet / 27.43 m) in the Royal Navy and many navies worldwide.
Anchoring depth rule: Ships typically anchor with a scope (ratio of chain length to water depth) of 5:1 to 7:1 for safety.
Example:
- Water depth: 10 fathoms (60 feet)
- Required chain: 50-70 fathoms (300-420 feet)
- That's 3.3 to 4.7 shackles
The Arpent is a historical French unit used primarily for measuring land area, but also sometimes used as a unit of length. As a unit of length, the arpent typically referred to the side length of a square arpent of land.
Its precise length varied significantly by region and time period in France and its colonies. A commonly cited value, particularly associated with the arpent de Paris, is based on 180 French feet (pieds du Roi), which equates to approximately:
- 58.47 meters (m)
- 191.8 feet (ft)
Other variations existed, such as the arpent commun (based on 200 French feet, ~64.97 m) and the arpent d'ordonnance (based on 220 French feet, ~71.47 m).
Note: The Fathom is part of the imperial/US customary system, primarily used in the US, UK, and Canada for everyday measurements. The Arpent belongs to the imperial/US customary system.
History of the Fathom and Arpent
Ancient Maritime Practices (Pre-9th Century)
Mediterranean and Northern European sailors: Ancient mariners measured rope and depth using body-based units:
- Cubit: Elbow to fingertip (~18 inches)
- Pace: Two steps (~5 feet)
- Arm span: Outstretched arms (~6 feet)
Sounding lead: A heavy weight (lead sinker) attached to a marked line, dropped overboard to measure depth. Sailors counted arm spans as they hauled the line back aboard.
Old English Documentation (9th-11th Centuries)
Earliest references: Anglo-Saxon texts use "fæthm" for measuring rope lengths and describing distances.
Beowulf (8th-11th century): The epic poem mentions "fæthmas" in describing ocean depths and ship measurements.
Viking influence: Old Norse "faðmr" (similar arm-span measurement) influenced English usage through Viking contact and trade.
Medieval Standardization (13th-15th Centuries)
Edward I (1272-1307): English law under Edward I began standardizing measurements, including the fathom at 6 feet.
Admiralty regulations: The emerging Royal Navy needed consistent rope, sail, and depth measurements for shipbuilding and navigation.
Rope making: British rope makers sold cordage by the fathom, with standard lengths for anchor cables (120 fathoms = 1 cable length in some contexts).
Age of Exploration (15th-17th Centuries)
Navigation charts: Early nautical charts (portolan charts) began incorporating depth soundings in fathoms.
Captain James Cook (1768-1779): Cook's Pacific voyages produced meticulous charts with fathom-based depth measurements. His charts became templates for British Admiralty standards.
Example - HMS Endeavour soundings: Cook's logs record depths like "15 fathoms, sandy bottom" or "No bottom at 100 fathoms" (indicating depths exceeding 600 feet).
British Admiralty Charts (19th Century)
Hydrographic Office (founded 1795): The British Admiralty Hydrographic Office systematized global nautical chart production, standardizing fathoms for depth.
Matthew Fontaine Maury (1806-1873): American oceanographer Maury collaborated with the British to create standardized depth charts using fathoms, mapping ocean currents and depths.
Cable-laying expeditions: Transatlantic telegraph cable projects (1850s-1860s) required precise fathom-based depth surveys. HMS Agamemnon and USS Niagara charted the Atlantic floor in fathoms before laying the 1858 cable.
U.S. Navy Adoption (19th-20th Centuries)
Inherited British standards: The U.S. Navy adopted British maritime practices, including fathom-based charts and anchor cable measurements.
U.S. Coast and Geodetic Survey: Founded in 1807 (originally "Survey of the Coast"), it produced nautical charts in fathoms for American waters.
World War II: Submarine warfare and amphibious operations relied heavily on fathom-based depth charts. USS submarines operated in waters charted in fathoms.
Metrication Movement (20th Century-Present)
International Hydrographic Organization (IHO, founded 1921): Recommended global adoption of metric system for nautical charts.
Gradual transition:
- 1970s-1980s: Most nations began publishing new charts in meters
- UK Admiralty: Converted most charts to meters by the 1990s
- U.S. NOAA: Many American charts still use fathoms, particularly for coastal waters
Mixed usage today: Modern electronic chart systems (ECDIS) allow display in either fathoms or meters, accommodating mariners accustomed to either system.
The term "arpent" likely derives from the Gaulish arepennis, meaning "end of a field," suggesting its origins relate to agricultural land measurement, possibly representing the amount of land that could be plowed in a day. It became a fundamental unit for land surveying in France during the medieval period and remained in use until the adoption of the metric system following the French Revolution.
- Regional Variations: Before standardization efforts, the length (and thus area) of the arpent varied considerably across different regions of France. Key variations included:
- Arpent de Paris: Based on a perche (rod) of 18 pieds du Roi (French feet), with the linear arpent (side of the square) being 10 perches, totaling 180 pieds (~58.47 m). The area was 32,400 square pieds.
- Arpent Commun: Based on a perche of 20 pieds, linear arpent of 200 pieds (~64.97 m). Area: 40,000 square pieds.
- Arpent d'Ordonnance (or Arpent des Eaux et Forêts): Based on a perche of 22 pieds, linear arpent of 220 pieds (~71.47 m). Area: 48,400 square pieds. Used primarily for royal forests.
- Colonial Usage: The arpent was exported to French colonies, notably:
- New France (Quebec, Canada): The arpent de Paris became the standard for land grants along the St. Lawrence River, shaping the characteristic long, narrow farm plots (rangs).
- Louisiana (USA): The French arpent (usually the arpent de Paris) was used for land measurement before and sometimes after the Louisiana Purchase. Its legacy persists in land titles and some place names.
- Metrication: The metric system officially replaced the arpent and other traditional units in France in the late 18th and early 19th centuries, though its use lingered in practice and historical records.
Common Uses and Applications: fathoms vs arpents
Explore the typical applications for both Fathom (imperial/US) and Arpent (imperial/US) to understand their common contexts.
Common Uses for fathoms
1. Nautical Charts and Hydrography
Depth soundings: Nautical charts mark depths in fathoms, particularly on U.S. and older British charts.
Contour lines: Lines connecting equal depths (e.g., the 10-fathom line) help mariners avoid shallow areas.
Chart abbreviations:
- fms: Fathoms
- fm: Fathom
- No bottom at 100 fms: Depth exceeds 100 fathoms (600 feet)
2. Anchoring and Mooring
Anchor scope: Mariners calculate how much anchor chain to deploy based on water depth in fathoms.
Rule of thumb: Deploy 5-7 times the water depth in calm conditions, 7-10 times in storms.
Example:
- Depth: 8 fathoms
- Calm weather scope (5:1): 40 fathoms of chain
- Storm scope (10:1): 80 fathoms of chain
3. Commercial Fishing
Net depth: Fishermen describe trawl net depths in fathoms.
Example: "Running trawl at 50 fathoms" (300 feet deep)
Fishing line: Deep-sea fishing lines measured in fathoms to target specific depths.
4. Recreational Boating and Diving
Depth sounders: Many recreational boat depth finders display fathoms (though meters and feet are increasingly common).
Dive planning: Divers reference depth in fathoms on nautical charts when planning dive sites.
5. Submarine Operations
Periscope depth: Submarines traditionally use fathoms for depth control.
Example: "Dive to 20 fathoms" (120 feet)
Historical note: WWII submarine logs recorded depths in fathoms; modern submarines use meters.
6. Maritime Literature and Tradition
Nautical expressions:
- "To fathom something" = to understand its depth (metaphorically)
- "Unfathomable" = too deep to measure or comprehend
Sailing instructions: Traditional pilot books use fathoms for approach depths and anchorage recommendations.
When to Use arpents
The Arpent (both linear and area) is now largely obsolete for practical measurement but remains historically significant:
- Historical Land Surveys: Essential for interpreting old maps, deeds, and land grants in France, Quebec, Louisiana, and other areas formerly under French control (e.g., parts of the US Midwest like Missouri, Illinois, Indiana).
- Legal Context: Land descriptions in some regions may still reference original measurements in arpents, requiring conversion for modern understanding.
- Historical Research: Understanding the arpent is crucial for historians studying agriculture, settlement patterns, and land tenure systems in French history and its colonial contexts.
- Unit of Area: While this page focuses on the length, the arpent is more commonly known and encountered as a unit of area (the square arpent).
Additional Unit Information
About Fathom (fath)
How many feet are in a fathom?
Exactly 6 feet = 1 fathom.
This is the defining relationship. The fathom was standardized to 6 feet during medieval English measurement standardization.
How many meters are in a fathom?
1 fathom = 1.8288 meters (exactly).
This conversion uses the international foot definition: 1 foot = 0.3048 meters (exactly).
Calculation: 6 feet × 0.3048 m/ft = 1.8288 m
Is the fathom an SI unit?
No, the fathom is not an SI unit.
It belongs to the imperial and U.S. customary systems. The SI unit of length is the meter.
International usage: The International Hydrographic Organization recommends meters for nautical charts, but fathoms remain legal and common in U.S. and some British waters.
Is the fathom still commonly used today?
Yes, in specific maritime contexts, especially in the United States.
Still common:
- U.S. NOAA nautical charts (many coastal charts)
- Recreational boating in the U.S.
- Commercial fishing fleets
- Maritime tradition and literature
Declining usage:
- International shipping (uses meters)
- Most modern navies (switched to meters)
- New chart production (increasingly metric)
Result: Fathoms persist in American waters and traditional maritime communities but are gradually being replaced by meters in international contexts.
Where does the word "fathom" come from?
From Old English "fæthm" (outstretched arms, embrace).
Etymology:
- Proto-Germanic: *faþmaz (embrace, armful)
- Old English: fæthm (span of outstretched arms)
- Middle English: fadme, fathme
- Modern English: fathom
Original meaning: The distance between fingertips when a person extends both arms horizontally—roughly 6 feet for an average man.
Verb form: "To fathom" originally meant "to measure depth with outstretched arms," later metaphorically "to comprehend deeply" (exploring the depths of understanding).
Why are anchor chains measured in shackles, not fathoms?
Both are used, but shackles are standard for large vessels.
Shackle definition: 1 shackle = 15 fathoms = 90 feet = 27.43 meters
Reason: Anchor chains are physically connected with shackle links every 15 fathoms. These physical shackles allow disconnection for maintenance and provide visual/tactile markers when deploying chain.
Usage:
- Small vessels: Anchor chain length in fathoms
- Large vessels and navies: Anchor chain length in shackles
Example: "Deploy 5 shackles" = 75 fathoms = 450 feet of chain
How deep is "full fathom five"?
5 fathoms = 30 feet = 9.144 meters.
Shakespeare's The Tempest: Ariel's song describes a drowned man lying at the bottom, 5 fathoms below the surface.
Context: 30 feet is deep enough that:
- Surface light barely reaches the body
- Free diving without equipment is challenging
- The body would be difficult to recover without specialized equipment
This depth creates the eerie, unreachable quality of Ariel's description.
Can I convert my depth sounder from fathoms to meters?
Yes, most modern depth sounders (fishfinders, chartplotters) allow unit selection.
Typical options:
- Feet
- Fathoms
- Meters
How to change (general steps):
- Access settings menu
- Find "Units" or "Depth Units"
- Select preferred unit (fathoms, feet, or meters)
- Save settings
Check manual: Specific instructions vary by manufacturer (Garmin, Lowrance, Raymarine, Furuno, etc.).
What's the difference between fathoms and cable lengths?
Both are nautical length units, but they measure different things:
Fathom:
- 6 feet / 1.8288 meters
- Primarily for depth measurement
Cable length:
- UK: 608 feet = 185.3 meters (1/10 nautical mile)
- US (historical): 720 feet = 219.5 meters (120 fathoms)
- Primarily for horizontal distance (anchor cable, ship-to-ship spacing)
Confusion: The term "cable" sometimes referred to 100 or 120 fathoms of anchor cable, but the standardized "cable length" unit differs from this.
Do submarines still use fathoms?
Historically yes, but modern submarines use meters.
World War II era: U.S. and British submarines recorded depths in fathoms (e.g., "Dive to 50 fathoms").
Modern practice:
- U.S. Navy: Switched to feet and meters for submarine operations
- International: Nearly all modern navies use meters
Reason for change: International standardization, digital instrumentation, and NATO interoperability drove metrication.
About Arpent (arpent)
Is the Arpent a unit of length or area?
The Arpent is primarily known as a unit of area, representing a specific parcel of land. However, a linear arpent also exists, defined as the side length of a square whose area is one arpent. This page focuses on the linear arpent. The relationship is direct: Area Arpent = (Linear Arpent)². Because the linear arpent varied, the area also varied.
Where is the Arpent still relevant?
The Arpent is not used for everyday measurements today. Its relevance is almost entirely historical and legal:
- Quebec (Canada): Crucial for understanding historical land division and property lines, especially the seigneurial system.
- Louisiana (USA): Important for interpreting land titles dating back to the French colonial period.
- France: Relevant for historical studies and understanding old documents.
- Other former French territories: May appear in historical records (e.g., Mauritius, parts of the US Midwest).
How long is a linear Arpent?
There is no single value, as it varied regionally. Common historical values include:
- Arpent de Paris: ~180 French feet ≈ 58.47 meters ≈ 191.8 feet (Most common in Quebec & Louisiana)
- Arpent Commun: ~200 French feet ≈ 64.97 meters ≈ 213.2 feet
- Arpent d'Ordonnance: ~220 French feet ≈ 71.47 meters ≈ 234.5 feet (Note: The French foot, pied du Roi, was slightly longer than the English foot, approx. 32.48 cm or 12.79 inches).
How does the linear Arpent compare to a Meter or Foot?
- The most common linear arpent (~58.47 m) is significantly longer than a meter. (1 Arpent ≈ 58.47 m)
- It is also much longer than a foot. (1 Arpent ≈ 191.8 ft)
Is the Arpent an SI unit?
No, the Arpent is not an SI unit. It is a traditional unit from the French system of measurements. The SI base unit for length is the meter (m), and the SI unit for area is the square meter (m²).
Conversion Table: Fathom to Arpent
| Fathom (fath) | Arpent (arpent) |
|---|---|
| 0.5 | 0.016 |
| 1 | 0.031 |
| 1.5 | 0.047 |
| 2 | 0.063 |
| 5 | 0.156 |
| 10 | 0.313 |
| 25 | 0.782 |
| 50 | 1.564 |
| 100 | 3.128 |
| 250 | 7.819 |
| 500 | 15.639 |
| 1,000 | 31.277 |
People Also Ask
How do I convert Fathom to Arpent?
To convert Fathom to Arpent, enter the value in Fathom in the calculator above. The conversion will happen automatically. Use our free online converter for instant and accurate results. You can also visit our length converter page to convert between other units in this category.
Learn more →What is the conversion factor from Fathom to Arpent?
The conversion factor depends on the specific relationship between Fathom and Arpent. You can find the exact conversion formula and factor on this page. Our calculator handles all calculations automatically. See the conversion table above for common values.
Can I convert Arpent back to Fathom?
Yes! You can easily convert Arpent back to Fathom by using the swap button (⇌) in the calculator above, or by visiting our Arpent to Fathom converter page. You can also explore other length conversions on our category page.
Learn more →What are common uses for Fathom and Arpent?
Fathom and Arpent are both standard units used in length measurements. They are commonly used in various applications including engineering, construction, cooking, and scientific research. Browse our length converter for more conversion options.
For more length conversion questions, visit our FAQ page or explore our conversion guides.
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⚖️ Metric vs Imperial
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⚠️ Common Mistakes
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All Length Conversions
Other Length Units and Conversions
Explore other length units and their conversion options:
- Meter (m) • Fathom to Meter
- Kilometer (km) • Fathom to Kilometer
- Hectometer (hm) • Fathom to Hectometer
- Decimeter (dm) • Fathom to Decimeter
- Centimeter (cm) • Fathom to Centimeter
- Millimeter (mm) • Fathom to Millimeter
- Inch (in) • Fathom to Inch
- Foot (ft) • Fathom to Foot
- Yard (yd) • Fathom to Yard
- Mile (mi) • Fathom to Mile
Verified Against Authority Standards
All conversion formulas have been verified against international standards and authoritative sources to ensure maximum accuracy and reliability.
National Institute of Standards and Technology — Official US standards for length measurements
Bureau International des Poids et Mesures — International System of Units official documentation
Last verified: February 19, 2026