Acres, Sections, and Square Miles: The US Public Land Survey System
640 acres = 1 square mile = 1 section. 36 sections make a township. This is how most of the US west of Ohio was surveyed and sold.
Updated April 2026
Full section
640 ac
27,878,400 sq ft
1 mile x 1 mile
Half section
320 ac
13,939,200 sq ft
1/2 mile x 1 mile
Quarter section (Homestead Act)
160 ac
6,969,600 sq ft
1/2 mile x 1/2 mile
Quarter-quarter ('back 40')
40 ac
1,742,400 sq ft
1/4 mile x 1/4 mile
The PLSS in 60 Seconds
The Public Land Survey System was created by the Land Ordinance of 1785 to systematically survey the US territories west of the original 13 states and make them available for sale and settlement. It is still in use today and governs land descriptions across most of the western and midwestern United States.
Township
A 6-mile by 6-mile square block of land (36 square miles = 23,040 acres). Townships are identified by a north-south township number (e.g. T 5 N) and an east-west range number (e.g. R 7 E) relative to a principal meridian.
Section
A 1-mile by 1-mile square within a township. There are 36 sections per township, numbered 1-36 in a boustrophedon (back-and-forth) pattern starting in the northeast corner.
Quarter section
A section divided into four 160-acre quadrants (NE, NW, SE, SW). This was the standard Homestead Act grant of 1862.
Quarter-quarter section
A quarter section divided again into four 40-acre parcels. 40 acres = the 'back 40' or 'lower 40' of US farming tradition.
Reading a Legal Description
NW 1/4 of Section 14, T 5 N, R 7 E of the 6th P.M.
The northwest quarter-section of the named section. This is the 160-acre quadrant in the northwest.
The 14th section of the township. Section 14 is in the second row from the north, third column from the east in the standard PLSS zigzag numbering.
Township 5 North - the 5th township north of the baseline.
Range 7 East - the 7th range east of the principal meridian.
The 6th Principal Meridian, the north-south reference line for Colorado, Wyoming, Nebraska, and Kansas.
Where the PLSS Applies
PLSS applies
Most states west of Ohio and north of Texas, including the Louisiana Purchase states, Northwest Territory states, California, Oregon, Washington, and Alaska (variant).
PLSS does not apply
The original 13 states, Texas (retained its land under the annexation treaty), most of Kentucky and Tennessee (metes and bounds), Hawaii.
Square Miles to Acres - Quick Reference
| Square Miles | Acres |
|---|---|
| 0.0625 | 40 |
| 0.25 | 160 |
| 0.5 | 320 |
| 1 | 640 |
| 4 | 2,560 |
| 9 | 5,760 |
| 36 | 23,040 |