Astronomical Unit to Arpent Conversion Calculator: Free Online Tool

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).

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.

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).