An arpent is a measurement and has nothing to do with the condition of land. An arpent is about 192 feet in length but is also used to specify a quantity of land such as an acre. I believe the quantity of an arpent would be a square arpent but the word square is not used.
In the early days of New France everyone wanted and needed land with river frontage. So most lots were 2 or 3 arpents of frontage. These lots went back 20 to 40 arpents.
If you drive from Québec City to Ste-Anne or around the Isle d'Orléans, you can see the fence lines that still conform to those measurements. In many cases descendants of the original owners are still on the property.
12 linge = 1 Pouce 18 Pied = 1 Perche
12 Pouce = 1 Pied 180 Pied = 1 Arpent
6 Pied = 1 Toise A lieue(League) = 3.1 miles
Arpent Carrée = 0.846 Acres This was usually simply called an Arpent so you must know the
context in which arpent was used.
Pied 1.066 feet
Toise 6.396 feet
Arpent 191.88 feet
Most of the above is from "Our French-Canadian Ancestors" by Laforest. The table is in Vol 1 Appendix B1 and Vol 22 page 273(Same as Vol 1) Also in Vol 1 Appendix D2,3,4 are maps of the property lines through Chateau-Richer, L'Ange Gardien, and Ste-Anne in 1680. I'm sure you have some ancestors there.
This information courtesy of Ray Roux of Mexico, New York.