Home square footage calculator for listings

• L shape: type the full outside length and width, then the size of the corner that is missing. The calculator takes the corner away from the rectangle.
• Several rectangles: split an odd room or an open plan into rectangles and type each one. Kitchen and dining area together, for example.
• Triangle: base times height, divided by two. Useful for a corner cut at an angle; add it to the room as its own row.
• Area known: when the plan already gives a room's area, type it directly.

Listings separate the space people live in from the rest. Bedrooms, living rooms, kitchens, bathrooms, halls and other finished rooms are living area. Garages, unfinished basements, storage outside the home, porches, balconies and terraces are usually listed apart, or not at all. The calculator shows the two side by side, and the total of every room you entered.

Each room counts in full by default. Where a rule counts part of a space, type the share: in some countries a balcony counts at a quarter or a room with a low ceiling at half. Use the rule that applies where the home is, and leave the share at 100 when no rule asks for less.

These figures are measured inside the rooms. Walls, stairs and hallways between rooms take space too, so a figure measured from the outside of the walls, as the US standard asks, is larger than the sum of the rooms.

The American National Standard for measuring single-family homes is ANSI Z765 (Square Footage, Method for Calculating; the current edition is from 2021). Since April 2022 Fannie Mae has required appraisers to use it for houses, townhomes and other single-family homes whenever the appraisal includes an interior and exterior inspection, so it is the figure most lenders' appraisers work to.

Under the standard, a home is measured from the outside of its exterior walls, and only finished areas count. A finished area needs a ceiling of at least 7 feet. A room with a sloped ceiling counts if at least half of its floor has a 7-foot ceiling, and any part lower than 5 feet is left out. Finished space below grade is reported apart from the space above, and garages and unfinished areas are not part of the finished square footage. The result is reported to the nearest whole square foot.

A room-by-room total is the right tool for the description of each room and for a first figure. For the square footage you advertise, check with your MLS's rules, and for a figure a sale depends on, use a measurement made to the standard.

Divide the asking price by the living area: a home at $450,000 with 1,500 square feet of living area is at $300 per square foot. Enter the price here and the calculator shows it.

Compare it only with homes measured the same way, in the same area: a figure that includes the garage, or one measured inside the rooms against one measured from the outside, makes a home look cheaper or dearer than it is.

• Measure at floor level, wall to wall, and take each length twice: walls in older homes are rarely parallel. Use the shorter one, or split the room into rectangles.
• Leave out stairs, fireplaces and built-in cabinets only if the rule you follow says so; be consistent from room to room.
• Write down each room as you go, with the name you will use in the listing, so the list matches the photos and the floor plan.
• While you are in each room, shoot it in 360 too: one visit gives you the measurements and the photos for the tour.