Definition
An archaic Latin term appearing in early English legal texts as a variant spelling of PERCH — a unit of linear and land measurement equal to sixteen and one-half feet (also called a rod or pole). In land descriptions and conveyancing documents, perca denotes both the linear measure and, by extension, a square measure of land (a square perch, equal to 272.25 square feet, or one-160th of an acre). The term is encountered primarily in medieval and early modern records, particularly in metes-and-bounds descriptions, manorial surveys, and conveyances drafted in Latin or Law Latin.
Common Language
Modern common usage (Wiktionary): Perca is the genus name for freshwater perch fish (family Percidae), used in biological and taxonomic contexts.
Historical common usage (Webster's 1913): A genus of fishes, including the fresh-water perch.
The legal and common meanings are entirely unrelated. In law, perca derives from its Latin sense as a measuring rod or pole and has nothing to do with the fish. A researcher encountering perca in a land record should not be misled by the biological usage; the term is solely a unit of measure in legal and surveying contexts.
Common Confusion
PERCA, PERCH, ROD, and POLE all denote the same linear measurement of sixteen and one-half feet in English and American land law, and the terms are used interchangeably in historical records. PERCA is the Latinized or Law Latin form; PERCH is the anglicized version; ROD and POLE are the equivalent surveying terms. Confusion arises most often when researchers encounter perca in a medieval Latin deed and mistake it for a reference to the fish genus or fail to recognize it as a distance measurement. Separately, the square perch (a unit of area) must be distinguished from the linear perch (a unit of length); context — particularly whether acreage or boundary lines are being described — resolves which is intended.
Why It Matters in Research
Perca appears almost exclusively in pre-modern sources: Latin conveyances, manorial extents, Chancery rolls, and colonial-era land grants. Researchers working in Law Mind's historical deed and land records corpus should treat perca as a direct equivalent of perch and apply the standard conversion (16.5 feet linear; 272.25 square feet per square perch; 160 square perches per acre) when reconstructing boundaries or acreage from historical descriptions.
The spelling is unstable in older sources. Variant forms include pertica (the more classical Latin term for a pole or rod, and the more common form in medieval legal Latin), perca, and occasionally percha. Pertica is the term most frequently encountered in Domesday-era and medieval English Latin documents; perca appears in later Law Latin usage. Researchers using full-text search should run queries on all variants to avoid missing relevant passages.
Note that neither Black's edition directs substantive discussion to this headword — both entries consist solely of the measurement definition and a cross-reference to PERCH. Rapalje & Lawrence omits the term entirely (the entry reproduced in the source material is for an adjacent headword). This means historical dictionary support for perca as a standalone entry is thin, and the researcher is expected to follow the cross-reference to PERCH for fuller treatment.
No jurisdictional variation is relevant to the measurement itself, which was uniform in English law and carried into American colonial practice. However, some early American jurisdictions used the rod or pole in statutory form while older deed stock in the same jurisdiction retained perca in Latin descriptions, creating apparent inconsistency in the same chain of title.
Historical Dictionary Support
Black's Law Dictionary (both first and second editions) treats perca as a minor cross-reference entry, defining it only as "a perch of land; sixteen and one-half feet" and directing the reader to PERCH. This approach reflects the editors' judgment that perca has no independent legal content beyond its identity as a variant form of the more familiar English term. Rapalje & Lawrence provides no entry for perca, suggesting the compilers regarded it as too archaic or too derivative to warrant independent treatment by the late nineteenth century.
The Latin dictionary tradition (Lewis & Short) confirms that perca in classical Latin referred to the fish, not the measure; the legal measurement sense derives from pertica (a pole or rod), and perca in Law Latin represents a phonetic or scribal compression of that term rather than a direct classical borrowing. This distinction is invisible in the Black's entries, which provide no etymological context. Researchers relying solely on the Black's entry may not appreciate that pertica is the more authoritative and more common form in primary sources, and that perca is a later, less standard variant.