If you’ve ever flown over the American Midwest on a clear day, you’ve seen the "quilt." Thousands of perfectly straight lines carving the earth into giant squares. It’s almost hypnotic. Those squares aren’t accidental. They are the result of the Public Land Survey System (PLSS), a massive logic project started by Thomas Jefferson to make sure the government could sell off land without getting into a fistfight over every fence post. But if you're looking to buy property or just settling a bet, you need the hard number. So, how many acres are in a section of land?
The short, textbook answer is 640 acres.
But honestly? That’s rarely the whole story.
In the world of real estate and surveying, a "section" is basically a square mile. Since a square mile is 5,280 feet by 5,280 feet, you end up with 27,878,400 square feet. Divide that by the 43,560 square feet that make up a single acre, and you get exactly 640. It sounds clean. It sounds perfect. It’s the kind of math that makes sense on paper but gets weird the second you step into the mud.
Why "640 Acres" is Often a Lie
Nature hates a straight line. The earth is a sphere—mostly—and trying to lay flat, square grids over a curved surface is a geometric nightmare. Think about trying to wrap a gift box with paper that has a grid on it. Eventually, the lines bunch up or pull apart.
This is why we have "correction lines."
Surveyors back in the 1800s weren't working with GPS or LIDAR. They had chains. Actual metal chains. Because the North and South lines (meridians) converge as they move toward the poles, those "square" sections start to pinch at the top. To fix this, surveyors had to bake in "fractional sections." You might buy a section that is technically 638 acres, or maybe 642. If you’re looking at a plat map and see a section on the north or west side of a township, there’s a massive chance it isn't exactly 640.
It’s also worth noting that 640 is just the starting point for most rural land deals. Most people don't buy a whole section unless they are running a serious industrial farming operation or a massive cattle ranch. Instead, land is chopped up into "quarters."
A quarter-section is 160 acres. This was the magic number for the Homestead Act of 1862. The government decided that 160 acres was exactly what a single family needed to support themselves. If you’ve ever wondered why so many old farms are that specific size, that’s your answer. It was the "Goldilocks" zone of land ownership.
Breaking Down the Math (Without the Boredom)
Let's get practical. If a section is 640 acres, how do the smaller pieces look? You’ve probably heard terms like "the N 1/2 of the NE 1/4." It sounds like code, but it's just simple division.
- A Section: 640 acres (One square mile)
- Half-Section: 320 acres
- Quarter-Section: 160 acres
- Quarter-Quarter Section: 40 acres
That last one, the 40-acre plot, is where the phrase "the back forty" comes from. It’s literally the quarter-quarter section at the back of a farm.
Imagine a square. Cut it into four smaller squares. Those are your 160-acre quarters. Now, take one of those 160-acre squares and cut it into four again. You’re left with four 40-acre blocks. It’s a Russian Nesting Doll situation made of dirt and grass.
Modern surveyors use the Gunter’s Chain as the historical baseline for these measurements. A chain is 66 feet long. Why 66? Because 10 square chains equals exactly one acre. It’s an old-school hack that allowed people to calculate area in their heads without needing a calculator or a smartphone. An acre is also 1 chain by 10 chains (or 66 feet by 660 feet).
Real-World Land Buying and the "More or Less" Clause
If you are currently looking at a listing for a section of land, read the fine print. You will almost always see the phrase "640 acres, more or less."
That isn't just legal fluff.
It’s an admission that the physical boundaries—the fences, the creeks, the old stone markers—might not perfectly align with the theoretical grid. Roads are a huge factor here. Often, the "section line" runs right down the middle of a county road. If the county has an easement for that road, you might "own" 640 acres, but you can only actually farm or build on 630 of them.
Water also messes everything up. Accretion and avulsion—the fancy terms for when a river slowly moves or suddenly jumps its banks—can add or subtract land from a section over decades. If a river serves as your boundary, your "640-acre section" might be growing or shrinking every single year.
Beyond the Section: Townships and Ranges
To understand where a section lives, you have to zoom out. Sections are the building blocks of a Township.
A standard township is a 6-mile by 6-mile square. This means it contains 36 sections. When you’re looking at a legal description, it’ll say something like "Section 14, Township 3 North, Range 4 West."
Here is a weird trivia bit for you: The numbering of sections in a township follows a "boustrophedonic" pattern. That’s a fancy Greek word meaning "as the ox plows." You start at the top right (Section 1), go west to Section 6, drop down to Section 7, and head back east to Section 12. It zig-zags. If you just assumed Section 7 was right under Section 1, you’d be five miles off.
The Aliquot Parts System
Legal descriptions use "aliquot parts" to describe pieces of a section. It’s basically just describing a location by its relationship to the whole.
Let's say you want to buy 80 acres. In legal terms, that’s usually a "Half of a Quarter." It would be written as "The W 1/2 of the NW 1/4 of Section 22." To figure out the acreage of a long string like that, you just work backward from 640.
640 (Section) / 4 (NW 1/4) = 160.
160 / 2 (W 1/2) = 80.
It’s foolproof math, provided the section was 640 to begin with. But again, check those correction lines. In places like Montana or Kansas, where the grid is huge, those small discrepancies in the original 1800s surveys can lead to multi-million dollar lawsuits today if a pipeline or a wind farm is being installed.
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Why This Matters in 2026
We are seeing a massive shift in how land is valued. It’s not just about grazing or corn anymore. Now, it’s about carbon credits, solar arrays, and water rights.
A 640-acre section is a prime size for a utility-scale solar project. But developers don't just care about the total acreage; they care about the "topography" and the "setbacks." If your 640-acre section has a massive ravine through the middle, its "usable acreage" might only be 400.
On the flip side, for carbon sequestration contracts, every single square foot counts. Companies are now using satellite imagery to verify that the "640 acres" they are paying for is actually sequestering the amount of carbon promised. The "more or less" clause is getting a lot more scrutiny than it used to.
Common Misconceptions About Sections
A big mistake people make is assuming every "square" on a map is a section. In some states—especially the original 13 colonies—they didn't use the PLSS. They used "Metes and Bounds."
In places like Virginia or Massachusetts, land isn't a grid. It’s defined by "that big oak tree by the creek" or "the pile of rocks near Smith’s barn." In those areas, the concept of a "section" doesn't even exist. You just have parcels of random shapes. If you try to buy "a section" in Vermont, people will look at you like you have two heads.
Even in the West, you have "Spanish Land Grants." In states like Texas and California, old Spanish and Mexican land claims were honored. These often follow "Arpent" or "Vara" measurements and ignore the 640-acre grid entirely.
Actionable Steps for Land Owners and Buyers
If you’re dealing with a section of land, don't just take the 640 number at face value.
First, get a modern survey. If the last survey was done in 1950, it’s basically a guess compared to what we can do today. A modern surveyor will find the original "monuments"—usually brass caps or iron pipes—and use GPS to tell you exactly how many acres you’re working with.
Second, check for easements. Check the title for utility lines, road access, or drainage rights. You might pay taxes on 640 acres but only have control over 610.
Third, look at the ALTA survey. If this is a commercial or high-value purchase, an ALTA (American Land Title Association) survey is the gold standard. It shows everything—encroachments, fences that are in the wrong spot, and exactly where the "640" becomes reality.
Finally, understand the tax implications. Most counties tax you based on the acreage listed on the deed. If your deed says 640 but a new survey says 632, you might be overpaying on your property taxes. It’s a small difference annually, but over twenty years, that’s real money.
The 640-acre section is the foundation of the American landscape. It’s the reason our maps look like graph paper. But while the math is simple, the land itself is complex. Always verify the boundaries before you sign anything. Surface area is one thing; usable, legal acreage is another.