How to Calculate Square Feet, Even If Your Home Is a Hexagon

Whether you're selling your home or looking to buy, one concept that's crucial to understand is how to calculate square feet. After all, there's a huge difference between a home that's 400 square feet (tiny) and one that's 4,000 (McMansion), and not just in terms of how much space you've got to stretch your legs.

A home's square footage is a crucial element in determining the price of a home you're trying to buy or sell, how much you'll pay in taxes if you live there, and what kinds of renovations are possible in your future. Plus, a home's square footage can be surprisingly subjective.

Here's what you need to know to ace any square-footage pop quiz that comes your way.

Do the math

You probably know how to calculate the square footage of a simple room without any funny shapes. Just break out your measuring tape -- or a laser measure -- to get its length and width. Multiply the width by the length and voila! You have the square footage. Say a room is 20 feet wide by 13 feet long, then 20 x 13 = 260 square feet.

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Break down bigger spaces

While measuring a single room is no big deal, people get kind of intimidated when it comes to calculating the square footage of an entire home. While homes can initially seem "daunting to measure, they're just a collection of small boxes," says Mario Mazzamuto of SF Bay Appraisal. Don't sweat it if a room has an outcropping. Simply break that area down into a smaller box, and measure each box individually. Add up each box's square footage to get the room's total area. So if your living room, bedroom, bathroom, and hallway are 500, 400, 200, and 100 square feet respectively, that means the total is 500 + 400 + 200 + 100 = 1,200 square feet total.

If you have a round kitchen and a triangular rumpus room, fear not. Just check out vCalc's handy calculator that will compute square footage no matter what polygon's thrown your way. Once you choose a shape, the calculator will prompt you for the measurements needed to compute square footage.

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Take it all with a grain of salt

Now that you know how to calculate a home's square footage, it's time to bust your bubble with a big caveat: This figure is surprisingly subjective based on who's doing the measuring. For instance, you measured the actual, livable square footage between the interior walls. But many architects, however, measure the square footage from the exterior walls.

This explains why there are often discrepancies between your calculations and those of a Realtor, builder, or other sources.

"Many MLS services require a listing's square footage to come from a specific source," says Robin Kencel of Connecticut's Stevens Kencel Group. So while you can make your own estimate, you may need to hire a certain professional to come up with a number that can be used on your listing; check with your Realtor or town's building department to determine who that is.

As a general rule, "the square footage extends through the Sheetrock and framing to the exterior of the wall," says Mazzamuto. Generally, to do the same for your measurements, add 6 inches per measurement, he says.

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Watch: The Features That Help a Home Sell Fastest