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How to Calculate & Convert Acreage

Instructor: Ian Lord

Ian is a real estate investor, MBA, former health professions educator, and Air Force veteran.

Accurate calculation of acreage is an essential skill in describing the physical geography of a plot of land. In this lesson we will look at the formulas for determining the area of a piece of land, and converting that number into different units of meaurement.

Land Area Calculations

As a surveyor, Robert depends on accurate calculations to determine the exact size of a piece of land. The nature of land ownership and the need to maintain precise records requires accurate measurements. Since area can be expressed in many different units of measurement, it's an effective practice to scale the unit of measure to the size of the property. Which is simpler to imagine; 5,000,000 square feet or 117 acres? Let's take a look at some of the common calculations used to determine the area and perimeter of a plot of land, along with some of the common area references used in real estate.

Acreage Calculations

Since a lot of people don't typically think in acres, it's helpful for Robert to be able to explain just what an acre is. One acre is equal to 4,840 square yards or 43,560 square feet. This can also be visualized as a perfect square 208.7 feet on each side. We can begin measuring the area of a plot by measuring the base and height, also known as the length and width. A rectangular plot of land 100 feet wide by 400 feet deep acreage conversion formula would look like this:

Area = b X h

100 X 400 = 40,000 square feet

40,000 / 43,560 = 0.91827365

Plot = 0.92 acres

Area of a Trapezoid

But what if the plot isn't a perfect square or rectangle? Suppose the plot being measured is part of a cul-de-sac and is trapezoidal in shape. The side facing the street is 100 feet wide, and the back side of the property is 150 feet wide. The property is 200 feet deep. The formula for the area of a trapezoid is:

Area = ((a+b) / 2) X h

A = 100

b = 150

h = 200

(100+150) /2 X h= A

250/2 X h= A

125 X h = A

125 X 200 = A

24,400 Square Feet= Area

24,400 / 43,560 = 0.56014692

Plot = 0.56 acres

Area of a Triangle

A triangle shaped plot may be very unusual, but knowing how to calculate the area of a triangle allows Robert, our surveyor, another tool to measure irregular property shapes. Triangles can be used to measure plots with unusually angled property lines for example.

Picture a triangular section of a plot on top of an otherwise perfect square. The formula for the area of a triangle is (b X h) / 2, where b = the width of the triangle base, and H is the height of the triangle. If the base is 100 feet wide, and the height is 400 feet then:

(100 X 400) / 2 = A

40,000 / 2 = A

20,000 Square Feet = Area

20,000 / 43,560 = 0.45913682

Plot = 0.46 acres

Other Conversions

The following conversions are helpful in converting units of area into other units of measurement. Acres can be easily converted into square miles, sections, and townships. Sections and townships are measurements in the rectangular grid survey system. A section is equivalent to one square mile and a township is made up of a grid-work of 36 sections. Here are some of the formulas below:

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