Multi-Room Square Footage Calculator
Measure a house one room at a time. Each row takes its own shape, so a round bay window or a triangular attic corner adds to the same total as a plain rectangular bedroom.
How to calculate the total square footage of a house
Measure room by room and add the results. It is tempting to measure the outside of the building instead and save yourself the walk, but the two numbers are not the same: an exterior footprint includes the thickness of every wall, which on a typical house puts it 3% to 6% above the sum of the rooms inside. Mixing the two is the usual reason a homeowner's figure disagrees with the one on the listing.
Include hallways, landings, stairs and closets — anything you walk through or store things in counts as floor area. For a materials estimate, count whatever you are actually covering, and leave out any run of fitted cabinets you will not be flooring under.
Measuring an awkward room
Any floor plan can be broken into simple shapes. A room with an alcove is a rectangle plus a smaller rectangle; a room with an angled corner is a rectangle plus a triangle; a bay window adds a trapezoid. Add each piece as its own row and the total takes care of itself — which is also why the draw tool on the home page lets you place several rooms on one grid and drag their corners until the outline matches what you measured.
Where a room has a corner missing rather than an alcove added, the L-shape calculator subtracts the notch for you in one step.
When you need gross living area instead
If the number is going onto a property listing or into an appraisal, a plain total is the wrong figure. Use the gross living area calculator, which applies the ANSI Z765 rules: only finished, heated, above-grade space counts, a finished basement is reported separately, garages never count, and a stairwell opening is deducted from the floor above it.
Two guides go further: calculating square footage for multiple rooms covers open-plan spaces and avoiding double-counts, and the whole-house guide explains gross living area versus a plain total.
Frequently asked questions
How do I calculate the total square footage of a house?
Measure each room separately and add the areas together, including hallways, stairs and closets. Do not try to measure the whole floor in one go: an exterior measurement includes wall thickness that a room-by-room total does not, and mixing the two is the usual reason a homeowner's figure disagrees with the listing. Add each room as its own row here and the running total builds as you go.
Do hallways, stairs and closets count?
For a materials estimate, count anything you are covering, which normally includes hallways and closets. For a property figure, hallways and closets count as living area, and a staircase is counted once on each floor it serves — but the opening it passes through is subtracted from the floor above. That distinction is what the gross living area calculator handles.
Can I mix different room shapes in one total?
Yes. Each row takes its own shape, so a round bay window, a triangular attic corner and a plain rectangular bedroom all add into the same total. Measure any genuinely irregular room as two or more simple shapes and enter them as separate rows — the arithmetic is identical and it is far easier to check.
Why does my total differ from the figure on the listing?
Usually because the two are measuring different things. Listings quote gross living area, measured to the exterior walls and excluding garages, unfinished space and finished basements, while a room-by-room total measures interior floor only. The gap between them is roughly the wall thickness around the whole perimeter, which on a typical house is between 3% and 6%.