Calculate Footage

Measure your home inside and out

To obtain a gross idea of the square footage of an area, multiply the length by the width. It really doesn't matter whether you are calculating the size of your lot or the size of your living room unless you are trying to figure how much paint you need or how much space you have for a vegetable garden. Then getting a more accurate number becomes important.

Measuring your lot

How many square feet in an acre?

There are 43,560 square feet in one acre.

To determine the acreage size of your lot, divide the total square footage by 43,560.

For example, a lot is 110 feet wide by 115 deep.

  • 110 x 115 = 12,650 square feet
  • 12,650 ÷ 43,560 = 0.29 acre

If you have 110.25 acres:

  • 110.25 x 43,560 = 4,802, 490 square feet

Lots in cities tend to be square, however it is by no means uncommon for lots to be pie shaped or irregular, especially when plotted around a cul-de-sac or defined by a geographical feature such as a creek. The lot dimensions should form part of your mortgage package. When you purchased your home, the lenders certainly required the dimensions and lot size so they would know precisely what they were investing in. However, where those property lines are located can be an issue if your lot has not been recently surveyed. If you don't know where your property starts and ends, you may want to get that information nailed down, especially if you want to add a fence or wall. Even the best of neighbors can be mistaken about where the lot line is and if they mow on your side of the lawn for years, they may actually assume that they own property that rightfully belongs to you ... or vice versa.

So, assuming you know precisely where your property lines are, and the width of your lot is 55 feet and its depth is 110 feet (an ordinary city lot) then your lot is 6050 square feet or just shy of 0.14 acre (an acre being 43,560 square feet). In other words, you and six of your closest neighbors probably equal one acre if their lots are the same size as yours. This is a perfectly respectable lot size, however if your house is a 2500 sq. ft., single-story ranch, your lot may feel considerably smaller than if your home splits its total square footage between two stories. Such are the benefits of a smaller footprint.

Rectangles and triangles help determine square footage.
Rectangles and triangles help determine
square footage.

But what if your lot size is oddly shaped? How do you calculate square footage then? Probably the simplest means is to revisit your high school geometry lessons and break your lot into more easily calculatable elements. Your lot comprises rectangles, squares, and triangles. Even if math isn't your strong suit, it's not too difficult to lay out a series of rectilinear shapes and determine square footage. In the adjacent image, you can see how a series of rectangles have been imposed over an otherwise irregular shape. Where a diagonal bisects a rectangle, the total is divided by 2. All individual components are calculated, then added together to obtain the total.

Square footage of your home

Determining the actual square footage of your home is not as straightforward as you would expect. American National Standards Institute (ANSI) suggests that residential property be measured using exterior measurements of the building at each level. (For the purposes of figuring a home's square footage, room dimensions are irrelevant.) Keep in mind that ANSI standards (which are guidelines, not regulations) define finished spaces as any enclosed area that is used year around. Exclude any space that is not finished or heated like the main body of the house. Don't include the garage as part of your home's square footage, though you would count it when calculating its footprint relative to the property itself.

Measure the exterior of the building at the level of the floor. If a bumpout occurs at the floor level, include it. If it occurs higher like a cantilevered window with a window seat, do not include it as part of the square footage. Measure to the nearest inch or 1/10th of a foot as this makes calculating room sizes more accurate. To arrive at total square footage, multiply width by depth. Add bumpouts and subtract indentations. Subtract stairwells. For second floors that occur under a gabled roof, you'll need to measure inside.

For more detailed suggestions, see an old but still useful article by Chet Boddy.

Measuring rooms

There are a variety of good reasons to measure the rooms in your home. Buying enough paint, wallpaper, or flooring; arranging furniture; and calculating the type of home theater components are just a few.

A third dimension that often comes into play with rooms is ceiling height. Cubic area—that is, width x length x height—is used to calculate the size of air conditioning units and heat pumps.

Measuring cubic feet is the same as measuring square footage. A living room that is 15 x 14 x 8 feet is 1,680 cubic feet. For a room with a cathedral ceiling, the following illustration may help.

Calculating cubic feet

Calculating squares and cubes is manageable for most of us who have forgotten most of what we knew about the finer points of mathematics ages ago.

Measure twice

"Measure twice, cut once" is an old saying but which always holds true. Carry it a bit farther and keep a record of all the measurements of your home. It is incredibly useful to know sizes and dimensions of each window and room, especially when new carpet is on your short list and there is a smoking deal over a holiday weekend at your local carpet retailer's. It will save you the trip home to measure or the cost of ordering more than you need, just to be on "the safe side".


So you've measured correctly and purchased the carpet. To find a local carpet installer, use Next Step Remodeling Small Repairs .

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