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The square footage of a building is found in the same way as that of vacant land. However, many buildings are not simple rectangles but in essence a combination of rectangles. To find the square footage of a typical home may require dividing the home into its rectangular parts and adding them once each box or rectangle has been measured.

Gross Versus Net Area

With most commercial rental property, there are two areas that are important to know. The gross area is the total floor space of any building. This area can be found by taking the outside measurements of the building, finding each floor’s gross area, and multiplying that area by the number of floors.

For example, the outside measurements of a building 100 feet by 150 feel would give a gross floor area of 15,000 square feet.

100 ft. x 150 ft. = 15,000 sq. ft.

If the building had five stories and each floor was the same size, then multiplying the square footage of the one floor by the number of floors would give the total gross area of the entire building:

15,000 sq. ft. x 5 = 75,000 sq. ft.

This shows that the building has a total gross area of 75,000 square feet. If this was a rental building, note that not all the area in a building is rentable. There are corridors, stairwells, elevator shafts, equipment rooms, maintenance areas, and the  like. The size of each of these non-useable areas needs to be calculated and deducted from the gross area to arrive at the net rental area.

In a simple, single-story building, such as a strip shopping area or freestanding building, the gross area and the net rental area can actually be equal. In comparing the values of different properties, knowing the spread between the gross area and the net rental area can be important. Two buildings that appear identical, with the same gross area may vary substantially in the net rental areas. Because rents are usually based on the net rental area, a price comparison based just on gross area could be misleading. Everything else being equal, a greater net rental area would be worth more.