Land records · Parcel maps · October 5, 2026
What Is an Arpent? French Land Measurement
An arpent is a French unit of length and area used in Louisiana and the Mississippi Valley. A square arpent is about 0.85 acre. Conversions and long lots.
What is an arpent? An arpent is an old French unit used as both a length and an area measure. It appears in land records in Louisiana, parts of Missouri, Mississippi, Arkansas, Illinois, Indiana, Michigan, and other areas settled or granted under French rule. As a length, an arpent is about 191.8 feet. As an area, a square arpent is roughly 0.845 acres, about 36,800 square feet. This page is general land-records background, not legal advice.
Arpent conversions
| Unit | Approximate equivalent |
|---|---|
| 1 linear arpent | 191.8 feet, 180 French feet |
| 1 square arpent | 0.845 acres |
| 1 square arpent | 36,800 square feet |
| 1 acre | About 1.18 square arpents |
Exact values in historical documents can vary slightly, so surveyors check the standard used in each region.
French long lots
French colonial land was often divided into long, narrow lots fronting a river or bayou, giving each owner water access, a natural levee for homes, and back land for farming or timber. A typical description might read “4 arpents front on the river by 40 arpents in depth.” These long lots still show on parcel maps along the Mississippi and bayous, with property lines running back from the water.
Why arpents matter today
- Old titles: Louisiana and Missouri titles may trace back to French or Spanish grants measured in arpents.
- Lot shapes: long lots influence modern parcel lines and roads.
- Riparian boundaries: river front measurements interact with shifting water lines. See what is a riparian lot line.
- Confirmed claims: after the Louisiana Purchase, the United States confirmed many private claims, often documented in patents. See what is a land patent.
Converting arpent descriptions
- Determine whether the arpent is linear or square in each phrase.
- Convert frontage and depth to feet.
- Multiply to estimate area, then convert to acres.
Example: 2 arpents front by 40 arpents deep is 80 square arpents, about 67.6 acres.
Other historic units
Spanish varas and English rods and chains appear in records from other regions. See what is a vara and what is a rod in land measurement. Descriptions with arpents are often a form of metes and bounds. See metes and bounds vs lot and block.
Reading arpents on modern maps
Parcel maps in river parishes and counties often show long, thin parcels perpendicular to the river, sometimes subdivided many times through inheritance into very narrow strips. Comparing these shapes with old descriptions in arpents helps explain why property lines meet the road at odd angles or why a parcel is hundreds of feet long but only a few dozen feet wide.
Bottom line
An arpent is a French unit used as about 191.8 feet in length or about 0.845 acre in area. It appears in Louisiana and Mississippi Valley land records and explains the long, narrow river lots still visible on parcel maps. Explore long lots on the Platbookmapper map.
What is an arpent FAQ
How big is an arpent?
About 191.8 feet as a length, or about 0.845 acres as a square arpent.
Where are arpents used?
In Louisiana and areas once under French rule in the Mississippi Valley.
How many acres is a square arpent?
About 0.845 acres.
What are French long lots?
Narrow lots running back from a river, often described in arpents.
Are arpents still used today?
Mostly in historical descriptions and older titles.