The Walden Effect: Farming, simple living, permaculture, and invention.

How to estimate acreage of a property

Graph paper property boundaryYesterday, I explained how to map your property boundaries from a deed.  I told you to use a sheet of graph paper for your mapping, but didn't mention that the purpose of the graph paper is to make it easy to measure the acreage of your property.

Your first step is to figure out how much land area one square equates to.  My graph paper has four squares per inch and the scale of my map is one centimeter for every 200 feet, which means (using the math shown in the second image) that each square is equal to 127 feet on each side.

The area of the square is 127 feet times 127 feet, or 16,129 square feet.  Since one acre contains 43,560 square feet, one of my graph paper squares bounds 0.37 acres.

Now for the fun part --- counting squares!  First, count how many squares are entirely contained in your property boundary, making a mark Acreage mathinside each one so you don't double count it.  If you want to get a very accurate estimate (and spend all day at this project), you can then estimate the percent of each boundary square that's within your property, but I simply divide partial squares up into three categories --- those approximately 75% contained in the property, those half contained in the property, and those 25% contained in the property.  I count how many squares fit in each of these categories, putting a dot in each square once again as I count it. 

A little math shows that my property consists of approximately 154.25 squares, or 57.1 acres.  The deed listed the property as 57.72 acres, so it looks like my mapping and math were pretty good! 

You can use this same technique to estimate the acreage of parts of your property from a topo map or aerial photo.  For example, do you want to know how big that cleared area is?  Just figure out the scale, trace the boundaries onto a sheet of graph paper, and go to town.  Or you could use Google Planimeter....

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About us: Anna Hess and Mark Hamilton spent over a decade living self-sufficiently in the mountains of Virginia before moving north to start over from scratch in the foothills of Ohio. They've experimented with permaculture, no-till gardening, trailersteading, home-based microbusinesses and much more, writing about their adventures in both blogs and books.

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I love doing this kind of applied math!
Comment by Maggie Tue Jul 24 08:01:09 2012

If you already have all the numbers in a spreadsheet, and you can calculate the coordinates of the points, then calculating the area of a closed polygon is relatively straightforward. Based on the numbers you published, I get 57.48 acres.

Comment by Roland_Smith Tue Jul 24 12:40:37 2012

Maggie --- I enjoy it too. :-)

Roland --- Funny to hear that the real acreage is midway between my estimate and the deed's estimate.

For those reading along at home, you can download Roland's spreadsheet, fill in your own data, and plot your boundaries and measure acreage the easy way! Thanks so much for sharing that, Roland!

Comment by anna Tue Jul 24 15:41:44 2012

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