Sections · Township and range · Acreage · October 18, 2026

How Many Acres in a Section of Land? 640 and Its Parts

How many acres in a section? A standard section is one square mile, 640 acres. Acres in half, quarter and quarter-quarter sections, plus odd-sized ones.

How many acres in a section? A standard section of land is one mile on each side, one square mile, which works out to 640 acres. That is the building block of the township and range system used across most of the Midwest and West, and it is why farm and ranch land is so often sold in 640, 320, 160, 80 and 40 acre pieces. Real sections are not always perfect, though. This guide shows the math, lists the acreage of every common part of a section, explains why some sections come out bigger or smaller and covers how “section” works in places like Texas.

The short answer

Section: 1 mile × 1 mile = 1 square mile = 640 acres.
Half section: 320 acres. Quarter section: 160 acres. Quarter-quarter (a “forty”): 40 acres.
Township: 6 miles × 6 miles = 36 sections = 23,040 acres.
Those numbers are nominal. Sections along the north and west sides of a township, and sections cut by lakes or rivers, often hold more or less than 640 acres, and the odd pieces are mapped as numbered lots.

The math: why a section is 640 acres

A mile is 5,280 feet, so a square mile is 5,280 × 5,280 = 27,878,400 square feet. An acre is 43,560 square feet. Divide one by the other and you get exactly 640 acres in a square mile.

The federal Public Land Survey System, the rectangular survey that began with the Land Ordinance of 1785, was designed around that unit. Surveyors laid out townships about 6 miles square and divided each one into 36 sections of about one square mile. The Bureau of Land Management describes each section as nominally 1 mile square and 640 acres. The system covers 30 states, mostly west of the Appalachians; see section, township and range for how the grid is laid out and how sections are numbered.

Acres in each part of a section

Sections are split into halves and quarters, then halves and quarters of those. These pieces are called aliquot parts, and the acreage below is for a standard 640-acre section:

Whole section (Section 12): 640 acres, 1 mile × 1 mile
Half section (N 1/2 of Section 12): 320 acres, 1 mile × 1/2 mile
Quarter section (NE 1/4): 160 acres, 2,640 × 2,640 feet
Half of a quarter (S 1/2 NE 1/4): 80 acres, 2,640 × 1,320 feet
Quarter-quarter (NW 1/4 NE 1/4): 40 acres, 1,320 × 1,320 feet
Half of a quarter-quarter (E 1/2 NW 1/4 NE 1/4): 20 acres, 1,320 × 660 feet
Quarter-quarter-quarter (SW 1/4 NW 1/4 NE 1/4): 10 acres, 660 × 660 feet
Half of that: 5 acres, 660 × 330 feet

Each step to a quarter divides the acreage by four, and each step to a half divides it by two. So you can work out the nominal size of any aliquot description by starting at 640 and dividing from the end of the description back to the section. The NE 1/4 of the SW 1/4, for example, is 640 ÷ 4 ÷ 4 = 40 acres. More on quarters in what is a quarter section.

The quarter-quarter has a special place. Under the general federal land laws, BLM treats the 40-acre quarter-quarter, or a lot, as the smallest legal subdivision, which is one reason so much rural land changed hands in “forties.” Under the mining and reclamation laws, the smallest legal subdivision is the 10-acre quarter-quarter-quarter.

Why some sections are not 640 acres

The grid had to fit a round earth, real terrain and 19th century chains and compasses. Several things push actual sections away from 640 acres:

Converging meridians. North-south lines get closer together as they run toward the pole, so the grid cannot stay perfectly square. Surveyors reset the spacing along standard parallels, which is why rural roads sometimes jog at a correction line.
Excess and deficiency go to the north and west. By the standard plan, sections were surveyed from south to north and east to west, and any extra or missing distance was thrown against the north and west boundaries of the township. The sections along those two edges, numbers 1 through 7, 18, 19, 30 and 31, are the ones most likely to be irregular.
Lakes and rivers. Where water cuts a section, the dry land was measured along meander lines and surveyed into numbered pieces instead of neat quarters. See what is a fractional section.
Lots. The leftover pieces along township edges and water are labeled as lots, such as Lot 3 of Section 6, each with its own acreage on the official plat. These are what many people call government lots.
Old survey error. Original corners set by early surveyors control the boundaries even when their measurements were off, so a section can run long or short by a noticeable amount.

That is why a deed may say “the NE 1/4 of Section 6, containing 158.4 acres, more or less” instead of 160. When the exact figure matters, rely on the official survey plat, the deed and a current boundary survey rather than the nominal number.

How to find the acreage of a real section or parcel

Read the legal description. The section, township, range and aliquot part tell you the nominal acreage. See how to find a property’s legal description.
Check the county parcel record. Assessor cards usually list deeded or calculated acres for each parcel.
Open a county GIS parcel map with the PLSS layer turned on. Many viewers draw section and quarter lines so you can see where a parcel sits in its section. Our land map links to county parcel viewers, and rural parcel search by section, township and range walks through the lookup.
Look at the official survey plat. BLM’s original township plats show lot numbers and the acreage of irregular pieces.
Hire a surveyor if you are buying, selling or fencing by acreage. A GIS map is a good guide but not a survey. Our guide on how to find the acreage of a property covers the options.

Sections in Texas and other non-PLSS states

Texas never joined the federal rectangular survey, so its land is described by original surveys, abstract numbers and, in much of West Texas, by block and section within large railroad and other grant surveys. Those sections are still commonly about one square mile. The Texas General Land Office notes, for example, that the Texas Constitution of 1876 granted railroads 16 sections per mile of track at 640 acres to a section. But a Texas section is identified by survey, block and abstract rather than township and range, and its real acreage comes from its own field notes.

The original 13 states and several others, including Kentucky, Tennessee and West Virginia, mostly use metes and bounds descriptions, so “section” is not a standard land unit there. See what is metes and bounds. North of the border, western Canada’s Dominion Land Survey also uses one-mile sections of about 640 acres split into 160-acre quarter sections, with its own rules for road allowances and corrections.

Getting a feel for the size

A section is a square you could walk around in about four miles.
A quarter section is a half mile on each side, the classic 160-acre homestead.
A forty is a quarter mile on each side, about 1,320 feet.
A 10-acre piece is roughly 660 feet square, a little less than two football fields, end zones included, on each side.

Questions people ask

How many acres are in a section of land?

A standard section is one mile square, or one square mile, which equals 640 acres. Real sections can be a little larger or smaller because of survey adjustments, lakes and rivers.

How many acres are in a quarter section?

A quarter section is 160 acres, a square about half a mile, or 2,640 feet, on each side.

How many acres are in a quarter-quarter section?

A quarter-quarter section, often called a forty, is 40 acres, about 1,320 feet on each side.

How many sections are in a township?

A standard township is 6 miles square and contains 36 sections, for a nominal total of 23,040 acres.

Why does my deed say a quarter section has less than 160 acres?

Sections along the north and west edges of a township, and sections cut by water, absorb survey adjustments and are often irregular. Their odd pieces are mapped as numbered lots with their own acreage.

Is a section in Texas 640 acres?

Many Texas sections, especially in West Texas railroad block surveys, are about 640 acres, but Texas does not use the federal township and range system. Its land is identified by survey, block, section and abstract, and the real acreage comes from the original field notes.