So even in hilly terrain, the acre is measured as if the hill were cut off at the horizontal, parallel to the horizon. That is, the portion of the earth being measured is considered a horizontal plane.īy convention, then, land area is measured on a two-dimensional common surface plane projected onto the ground. And while it is possible to account for the curvature of the earth in land surveying, most boundary surveys for parcels less than a few hundred square miles use plane surveying. Whatever the shape of a parcel – or the topography of the land it contains – surveyors calculate its acreage based on a common surface, using basic geometry (whose Greek root words mean earth measure).

If you wanted to create a one-acre rectangular parcel of land with one side a mile long, then it would be 8.25 feet wide. The number and length of its sides can be anything, just so long as the total area they bound equals 43,560 square feet. It is fixed at 43,560 square feet but has no specific length, width, or shape.

If a particular one-acre parcel happens to be in the shape of a perfect square, its sides would be 208.71 feet each. Still today, an acre is fixed at 43,560 square feet. Multiply these to get 43,560 square feet of area.

That determined the long side of the rectangle, and the short side of this one-acre rectangle was 4 rods (66 feet). This furrow-long distance became the furlong, which was equal to 40 King’s rods (660 feet to commoners like us). It was a rectangle, whose length was determined by the distance the oxen could plow before needing a rest. In fact, the acre had specific dimensions because of this. Originally, it was the amount of land that could be plowed by a team of oxen in a day. An acre is a two-dimensional measure of land area. In other words, you’d need a bigger quilt to cover an acre of Vermont than you’d need to cover an acre of Kansas.īut they don’t measure an acre by measuring the size of the quilt needed to cover it. There is definitely a catch, however, in that not every measured acre contains the same amount of ground surface. This is due to long-standing conventions of land surveying and accepted procedures for determining ownership boundaries. Every acre contains the same measure of land regardless of whether it is steep, bowl-shaped, or the Great Plains.

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