There are many reasons you may want to know the square footage of your home. From assessing your home’s value or listing it for sale to selecting upgrades (like HVAC systems) or shopping for a new home, an accurate square footage number is important to know. While self-measured square footage isn’t always allowable for purposes like real estate transactions, it’s good information to have. Here’s how to measure one popular definition of your home’s square footage: the gross living area (GLA).

1. Sketch a rough floor plan of your home’s interior

Draw each floor separately and leave out unfinished areas and outdoor spaces. Ensure there’s plenty of space to jot down measurements on each room.

1. Break down each space into shapes

To measure complicated spaces, reduce them to separate rectangles. For example, an L-shaped room would be two rectangles. Where rectangles don’t work, triangles and circles can be used.

1. Measure the dimensions of the shapes

Break out your measuring tape (or laser measure) and measure the sides of the rectangular sections you created. For triangles, measure each side, and for circles, measure the radiuses (halfway across the middle). Round your measurements to the nearest half foot and jot them down on the corresponding parts of your sketch.

1. Calculate the area of each shape

Multiply the length and width of each rectangle to find its area in square feet. For other shapes, use this webpage to calculate their areas. Write these numbers down in the middle of each shape on your sketch.

1. Calculate the total square footage

Add up the area of each shape to find the total square footage of your home. Round your total to the nearest square foot.

Final notes

Depending on the standard used and your local real estate market, not all parts of your home should be included in your gross living areas. Garage space is excluded, and basements may not be counted, even if they’re finished. Finished, habitable attic space with at least seven feet of clearance should be included in your total.

When it comes to selling your home, your real estate agent will advise you on whether self-measured square footage can be used or if you must hire a professional to determine this number. Conversely, when shopping for a home, find out how the seller arrived at their number.

One popular source of discrepancies is the fact that architects and appraisers commonly use exterior rather than interior measurements to arrive at square footage numbers. To estimate your square footage by this standard, add six inches to each measurement from above, and recalculate your total area.

With a solid understanding of square footage, you can get the most from your home and ensure you know what you’re getting from your next one.