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Understanding Square Footage and Dimensions

When you buy a set of blueprints for a home, you get hundreds of dimensions and thousands of details. Before you buy the blueprints, you look at simplified “house plans” that give overall information about the blueprint. The house plans give you general information such as square footage and overall dimensions.

In this article, when we talk about rounding or approximations we are referring to the floor plans you see before you buy blueprints and not the actual details found on the blueprints.

Square Footage

A house plan's square footage tells you how many square feet of finished space a plan occupies. The finished space is the heated area of the home. Finished space usually has floor coverings such as wood, vinyl, ceramic, or carpeting.

Unfinished areas such as garages, porches, decks, attics, courtyards, and driveways are not included as part of the finished square footage of a plan. A basement is not included in the finished square footage unless the basement is finished. A 3-season porch is not considered finished square footage because it is not heated space.

Unfinished bonus rooms (such as a room over a garage) are not considered finished square footage. However if you finish the bonus space then it can be considered finished square footage. On our website we sometimes give a minimum and maximum square footage range for a floor. The minimum square footage shows the size of the floor if the bonus space is not finished. The maximum square footage shows the size if the bonus space is finished.

Square footage is not the same as the floor space. Typically the square footage is calculated by using the dimensions starting from the outside studs of the home’s exterior. The square footage doesn’t include exterior wall coverings such as brick, stucco or siding. The square footage does include space that is taken up by walls.

For example if the outside dimensions of a one story home are 20 foot by 50 foot then the home has a square footage of 1000. In this example, if the home's walls are 4 inches thick then about 47 square feet of the square footage is used up by the thickness of the exterior walls. Therefore, of the 1000 finished square feet in this home only around 953 feet of interior space exists and the exterior walls take up the rest of the "finished" space.

Cantilevered floors also affect square footage. A cantilevered (overhanging) room such as a bay window is counted as finished square footage if the floor joists are part of the cantilever. If a cantilevered space does not include floor space (such as boxed window) then the cantilevered area is not counted as part of the square footage. If a fireplace cantilevers then the square footage of the cantilever is counted as finished square footage on the floor that has the fireplace but not on other floors.

For stairways in a two-story home, usually the space occupied by the staircase is counted once when calculating square footages. However a few designers or builders consider a stairway transitional space and sometimes count it as square footage on both floors. The floor space of an interior balcony or loft is included in square footage calculations.

If you are comparing two plans that have the "same" finished square footage you may want to remember that wall space is part of the square footage. For example, if you see a one story home that has the same finished square footage as a two-story home, then the one story home will actually have more interior space. This is because the two-story home has another floor of exterior walls that are considered part of its square footage. Also a two-story home needs more space for hallways and stairways and the useable square footage of a two-story home is usually less when compared to a one-story home that has the same square footage.

Square footage does not include any area on a level where a floor has not been built. For example, if a two-story home has a family room with a two-story ceiling then the square footage of the main floor would include the family room space. However, on the second floor there is no useable floor space over the family room and there is just airspace. Therefore on the second floor the family room's square footage would not be counted as part of the square footage for the second floor.

A low ceiling can also reduce the finished square footage of a room. The parts of a room where the ceiling is less than 5 feet tall do not count as finished square footage. Also, typically at least 50% of a room needs to have a minimum ceiling height of 7 feet for the room to count as finished space. This guideline is usually used for tax or real estate purposes, but some builders or designers may consider areas with low ceilings as finished square footage if the room is finished.

Reading Dimensions

On floor plans, the width is usually shown first and the depth is shown next. For example if a room dimension is shown as 10’ x 12’ then the width is 10 feet and the depth is 12 feet. “Width” means measurements going from side to side. “Depth” means measurements going from the front to the back of the home.

When a floor plan gives the dimensions of a room, it shows the interior dimensions. Room dimensions are measured from interior wall to interior wall and are usually the same as the floor covering dimensions. However, in some rooms the room dimensions are larger than the floor space dimensions. For example kitchens and bathrooms have built in cabinets and fixtures that take up floor space. Other rooms such as the great room may also have built-in bookshelves or cabinets that take up floor space. Closet space is usually not included in a room’s dimensions.

House plan companies usually show room dimensions in feet and inches and the square footage dimensions to the nearest foot. Usually the room size given indicates the distance from one interior wall of the room to the interior room on the opposite side of the room. However, some designers describe floor plans by measuring from the middle of the wall stud. Some designers also round off the room size. Therefore the room size dimensions given on a floor plan may be around 4 to 6 inches different then the actual interior room dimensions given on the blueprint. Sometimes designers do this to discourage illegal usage of the floor plans and when you buy the blueprints you will get the exact dimensions on the blueprints.

If a room is not a traditional square or rectangular room such as a room that has angles or curves, then it is difficult to note room dimensions. In these cases the room dimension on the plan usually gives an overall rectangular dimension. For an unusually shaped room, the blueprints will give much more detailed dimensions to properly represent the room.

Most house plans show only ceiling heights that are different from the primary ceiling height of other ceilings on the same floor. For example, if the main floor has a ceiling height of 9 feet, then typically only rooms that are not 9 feet tall will have a ceiling height shown on the floor plan. When a ceiling height is shown it usually describes the highest point the ceiling reaches in the room. For example if a room has a cathedral ceiling then the ceiling height describes the height of the ceiling at the peak of the ceiling.

When giving width and depth dimensions for a home’s footprint, usually the width and depth is based on the exterior walls of the home. Roof overhangs or structures without a roof are typically not included in the overall width and depth dimension. For example, decks, exterior steps, gates, and fences are usually not included when describing the footprint size of the home.