Calculating Square Footage, Area, and Volume

This is not a math course. We consider it to be an awareness course. The lessons should help make you aware of the different real estate calculations that require math. Yes, you can use a calculator to determine most of the answers. If you’re a real estate agent, be prepared to determine the square footage of rooms, attics, and even building lots. If you’re a buyer, you’ll know what the figure means if a realtor, lender, or seller tosses out a number such as the gross income multiplier or the property tax millage.

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In real estate, determining square footage is perhaps the most commonly performed mathematical calculation. Square footage is normally determined by multiplying the length by the width. If the area happens to be a wall, you would multiply the height by the width. This formula works only if the area is a perfect rectangle. Most houses are not perfect rectangles. An addition to the livingroom might be eight feet wider than the rest of the house. The second floor might overhang the bottom floor by two feet in the front and back. That would make the second floor four feet wider than the bottom floor.

When an area is not a perfect rectangle, you normally have to divide the area into separate shapes such as squares, rectangles, triangles, or even circles. Building lots are often anything but a perfect rectangle. In many cases, no two measurements of the property are the same. The lot might be 200 feet wide at the front, 300 feet wide at the rear, 400 feet deep on the left side and 375 feet deep on the right side. If the shape of the lot or house is not a rectangle, you’ll need to figure out exactly what the shape is and apply the appropriate formula to determine its square footage. In the above example, you would divide the property into a triangle using the front width, a triangle using the rear width, and a rectangle.

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Perimeter is the distance around the outside of an area. To calculate the perimeter, you simply add the lengths of the sides together. In our example above the lot was 200 feet wide at the front, 300 feet wide at the rear, 400 feet deep on the left side, and 375 feet deep on the right side. The perimeter of the lot would be 200 + 300 + 400 + 375 or 1,275 linear feet.

In real estate you might hear the terms builder’s acre and survey acre.  In construction and real estate development, the unit of measure is often the builder’s acre. A builder’s acre is 40,000 square feet. A survey acre or true acre is 43,560 square feet. If you’re moving from the country where an acre means a survey acre to a suburb where an acre means a builder’s acre, you’ll be short changed by 3,560 square feet for every acre you purchase. Most old timers and country landowners will tell you that an acre is 43,560 square feet. Most realtors will disagree and claim that an acre is 40,000 square feet. Both are technically correct. If you’re buying or selling large plots of land, make sure you know whether the unit of measure being used is the builder’s acre or the survey acre.

Volume is the total area inside a shape. The volume of a swimming pool would be the total area inside the pool. Volume is calculating by multiplying the length, width, and height. If the swimming pool is 20 feet long, 12 feet wide, and 8 feet deep, the total volume would be 20 x 12 x 8 or 1,920 cubic feet. This formula is useful for determining the volume of areas to be filled or excavated. Air conditioning and heating systems are often rated for the cubic feet of living space they can handle. Let’s say you want to dig a swimming pool the size of the one mentioned above. You could inform the excavator that the hole would be approximately 1,920 cubic feet. Or if you purchased a home with the same-sized pool, you could call a pool filling company and order 1,920 cubic feet of water. Of course, if you live in a city you probably had no idea you can order pool water to be delivered until you read the above example!


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