The difference between a half section and a full section comes down to size: a full section is one square mile of land containing 640 acres, and a half section is exactly half of that, 320 acres. Both are standard units in the Public Land Survey System (PLSS), the federal grid used to describe most land from Ohio westward, and both show up routinely in deeds, title reports, and rural land listings.
The Full Section
A full section is a square parcel measuring one mile on each side, or 5,280 feet by 5,280 feet. That area equals 640 acres. Every PLSS township contains 36 sections arranged in a six-by-six grid.1U.S. Geological Survey. Do US Topos and The National Map Have a Layer That Shows the Public Land Survey System
The 640-acre figure is the design ideal. Surveying references often qualify it with the word “nominally” because real sections on the ground don’t always hit that number exactly, for reasons covered further down.
The Half Section
A half section is 320 acres, created by drawing a single straight line through the middle of a full section. That line runs either north-to-south or east-to-west, producing two equal rectangles. Each half is identified by its position within the section: the North half (N 1/2), South half (S 1/2), East half (E 1/2), or West half (W 1/2).2Bureau of Land Management. BLM Module 2 Study Guide – The Public Land Survey System
The shape depends on how the section is cut. A north-south split (producing an East half and a West half) gives you a parcel one mile long and half a mile wide. An east-west split (producing a North half and a South half) gives you the same acreage in the opposite orientation: half a mile tall, one mile wide. Either way, the area is 320 acres.
So the practical difference between a half and a full is straightforward:
- A full section is 640 acres, one mile square.
- A half section is 320 acres, one mile by half a mile.
- A full section stands alone in a legal description by its section number; a half section always carries a directional prefix (N, S, E, or W) telling you which half.
How a Half Section Appears in a Legal Description
PLSS legal descriptions read from most specific on the left to most general on the right. For a half section, there is only one layer of subdivision, which keeps the description short. For example:
N 1/2, Section 14, T3N, R2W
Reading right to left: T3N, R2W identifies the township, three north and two west of the reference lines, which narrows you to a 36-square-mile block. Section 14 locates the specific one-square-mile, 640-acre section inside that township. N 1/2 then points to the northern 320 acres of that section.
A full section description simply omits the directional prefix: “Section 14, T3N, R2W” refers to all 640 acres. If you see no N, S, E, or W in front of the section number, you’re looking at the whole thing.
Half sections can themselves be subdivided further. The PLSS continues to halve and quarter down to quarter sections (160 acres), quarter-quarter sections (40 acres, the BLM’s standard land management unit), and smaller parcels described by stacking the prefixes.3Bureau of LandAment. BLM Module 2 Study Guide – The Public Land Survey System For the half-versus-full question, though, those smaller units are just further splits of the same underlying section.
Why the Acreage May Not Be Exact
The PLSS lays a flat grid onto a curved planet, and that produces unavoidable error. Meridians converge as they run north, so the north boundary of a section is slightly shorter than its south boundary. At 40° north latitude the difference is about 1.69 links (roughly 13 inches) per mile; at 70° north it grows to more than 5.5 links.4Bureau of Land Management. Manual of Surveying Instructions 2009 Over a six-mile township, the shortfall adds up.
Surveyors handled the problem by pushing the excess and deficiency into sections along the north and west edges of each township. Those sections come out slightly oversized or undersized, and any parcels inside them that don’t equal a standard 40-acre unit are designated as “government lots” rather than regular aliquot parts.2Bureau of Land Management. BLM Module 2 Study Guide – The Public Land Survey System Government lots also appear where a section borders a navigable river or lake and the grid can’t produce clean 40-acre parcels.
The BLM’s training materials put it plainly: “not all sections contain 640 acres, which is contrary to the plan of the rectangular system.” If you’re buying property, the acreage listed in the legal description may not match the actual surveyed acreage, especially on the north or west edge of a township or along a shoreline. A current survey is the only way to know exactly what you’re getting, and by extension what a half of that section really contains.
Where These Terms Apply
Sections and half sections are PLSS vocabulary. The system covers roughly 30 states, mostly from Ohio westward. The original 13 colonies and a handful of later states, including Texas and Hawaii, were never surveyed under the PLSS and don’t use section-based descriptions at all. Those states use metes and bounds, which defines boundaries by distances, compass bearings, and physical landmarks such as creeks, walls, or named trees.5Bureau of Land Management. Specifications for Descriptions of Land
If a deed refers to the “N 1/2” or “SW 1/4” of a numbered section, you’re in a PLSS state and the half-versus-full distinction is live. If the deed describes the property by its distances from landmarks and its compass bearings, section terminology doesn’t apply to that parcel.
Quick Reference
- Full section: 640 acres, 1 mile by 1 mile (5,280 ft by 5,280 ft).
- Half section: 320 acres, 1 mile by 1/2 mile, labeled N 1/2, S 1/2, E 1/2, or W 1/2.
- Quarter section: 160 acres, 1/2 mile by 1/2 mile.
- Quarter-quarter section: 40 acres, 1/4 mile by 1/4 mile.
These are the ideal figures. Convergence, survey adjustments, and water boundaries all create variation, so the number on the deed and the number on a modern survey may not line up exactly.