# Acres
**URL:** https://boards.straightdope.com/t/acres/62114
**Category:** Factual Questions
**Created:** [April 16, 2001, 2:24am UTC](https://boards.straightdope.com/t/acres/62114 "2001-04-16T02:24:58Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)
#### Post date: [April 16, 2001, 2:24am UTC](https://boards.straightdope.com/t/acres/62114/1 "2001-04-16T02:24:58Z")
How are acres measured? Assume there is a steep hill. Is the acreage measured on lines along the ground; or by geographic coordinates? That is, are you buying the hypoteneuse; or the base of the triangle?
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### Author:  [@bare](https://boards.straightdope.com/u/bare)
#### Post date: [April 16, 2001, 2:28am UTC](https://boards.straightdope.com/t/acres/62114/2 "2001-04-16T02:28:04Z")
An acre is 208.6 feet by 208.6 feet, measured on the level.
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### Author:  [@bare](https://boards.straightdope.com/u/bare)
#### Post date: [April 16, 2001, 2:34am UTC](https://boards.straightdope.com/t/acres/62114/3 "2001-04-16T02:34:39Z")
In other words, the base, not the hypotenuse.
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### Author:  [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)
#### Post date: [April 16, 2001, 12:48pm UTC](https://boards.straightdope.com/t/acres/62114/4 "2001-04-16T12:48:29Z")
> [@](#):
>
> In other words, the base, not the hypotenuse.
Thanks. I assume that the degree of any slope doesn’t matter?
My dictionary defines it as 160 square rods, 4,840 square yards, and 43,560 square feet. Taking the sqaure root of any of those numbers yields an irrational number. It would seem that an acre was not meant to be square, but 16 rods by 10 rods or some other measurement. (I know that a parcel can be any shape, but I was keeping it simple.) Of course when you’re talking about real estate, I guess inches aren’t that important; but acres and rods seem rather unwieldy. How did we come up with the acre, anyway?
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### Author:  [@frobozz](https://boards.straightdope.com/u/frobozz)
#### Post date: [April 16, 2001, 1:02pm UTC](https://boards.straightdope.com/t/acres/62114/5 "2001-04-16T13:02:30Z")
> [@](#):
>
> \*Originally posted by Johnny L.A. \*
> \*\*Taking the sqaure root of any of those numbers yields an irrational number. It would seem that an acre was not meant to be square, but 16 rods by 10 rods or some other measurement.
>
> \*\*
Yup.
An acre is a rectangle that is 4 x 40 rods, or 66 x 660 feet. I don’t know exactly where this comes from, although I remember hearing something about a rod being the width of a plow. (sounds suspiciously like roman chariot ruts determining railroad gauge to me.)
The rod was really the basic unit of land back in the day - most road rights-of-way that were laid out before the twentieth century are 33 or 66 feet wide - 2 or 4 rods.
And as for your original question - elevation does not matter at all in land survey. If you look at a survey map or a tax assesment map, all you see is a closed line representing the property boundaries. The legal description reads, “Beginning at a point and thence xx degrees north and xx degrees east a distance of xx feet to another point, thence…”
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### Author:  [@Duck\_Duck\_Goose](https://boards.straightdope.com/u/Duck_Duck_Goose)
#### Post date: [April 16, 2001, 1:12pm UTC](https://boards.straightdope.com/t/acres/62114/6 "2001-04-16T13:12:29Z")
An acre was originally the amount of land an ox could plow in one day. Oxen walk a lot slower than horses. Visualize a cow plodding along.
[http://hv.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg\_id=004JDX](http://hv.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=004JDX)
> [@](#):
>
> How did an acre come to be an acre? It was the amount of land one man and one ox could plow in one day. It was a standard used for planning purposes. If you had to have 40 acres plowed in four days, then you needed ten teams. One man with a tractor and plows or disks can now do several hundred acres in a day. Some for harvesting.
When you buy hillside acreage, you’re buying the flat part, not a cross-section chunk of the hill. Visualize a 1/2 acre tablecloth, spread out on the ground. So the degree of slope doesn’t make any difference.
An acre isn’t necessarily a perfect square, or a tidy rectangle, but a total number of square footage. It can come in different shapes. The world is full of oddly shaped parcels of land that are nevertheless measured in “square” feet and acres. Think of your nearest state park–it’s not usually a big tidy rectangle, but it’s still measured in acres.
“Filter strips” are long skinny rectangular acres.
[http://wcp.wsu.edu/fotg/section4/393.html](http://wcp.wsu.edu/fotg/section4/393.html)
Here’s an ad for a 684 acre farm. It’s not necessarily all in one big square chunk. You add up all the square footage and figure out how many acres that comes out to.
[http://www.eaglestar.net/Eagle/emm.html](http://www.eaglestar.net/Eagle/emm.html)
There are special courses that real estate appraisers and tax assessors take to learn how to do this.
[http://www.okstate.edu/ceat/clgt/classes.htm](http://www.okstate.edu/ceat/clgt/classes.htm)
> [@](#):
>
> Basic Mapping (12 hours)
> Similar to a three-day course required by law for Assessors, this course details how land is platted and surveyed and how this information is applied to mapping of tracts. Figuring acreage, determining lengths and various measures are just a few of the things covered in this very practical course.
When they figure out your acreage for tax assessment purposes, try to make sure they don’t include part of the road out in front, too. Judging by the Google hits for “appraisal figuring acreage”, this is a chronic “include or not include” question.
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### Author:  [@bare](https://boards.straightdope.com/u/bare)
#### Post date: [April 16, 2001, 1:27pm UTC](https://boards.straightdope.com/t/acres/62114/7 "2001-04-16T13:27:49Z")
Surveyors realized a long time ago that the metric system made more sense than feet and inches, problem is, they invented a convoluted way to measure in tenths.
Most public land surveys were measured in rods and Gunter chains. 1 rod=10 chains, 1 chain=66 feet,and can be further divided up into links which are 7.92 inches long.
1 acre=10 sq. Gunter’s chains = 160 rods = 43560 sq. ft.
Why do I remember all this crap?