Square Footage Calculator
Add up the total square footage of a house, apartment or floor plan from several rooms at once, with the cost at any price per square foot.
How to use this calculator
- 1List each room on its own line as length x width — an optional label before a colon keeps the breakdown readable.
- 2Set the unit you measured in. Mixing feet for most rooms and metres for one is fine — just be consistent within a single line.
- 3Add a price per square foot to turn the total into a cost estimate for flooring, paint coverage, or a rough listing value.
How the calculation works
Room area = length × width
Total square footage = Σ (room areas)- length, width
- Each room's inside dimensions
- Σ
- Sum across every room entered
Every room is converted to feet before multiplying, so metres, inches and yards can all appear in the same list.
This sums simple rectangles. An L-shaped or irregular room should be split into two or more rectangular lines and entered separately, the same way a flooring estimator would measure it on site.
Worked example
A 5-room floor plan
- 1.Living room: 20 × 15 = 300 sq ft.
- 2.Kitchen: 12 × 10 = 120 sq ft. Bedroom 1: 14 × 12 = 168 sq ft. Bedroom 2: 11 × 10 = 110 sq ft. Bathroom: 8 × 5 = 40 sq ft.
- 3.Total: 300 + 120 + 168 + 110 + 40 = 738 sq ft.
Result: 738 sq ft across 5 rooms
What "square footage" actually measures
Square footage is simply floor area — the amount of horizontal surface a room or a whole home covers, expressed in square feet. It is a two-dimensional measurement, so it says nothing about ceiling height, layout, or how usable the space actually feels; two rooms of identical square footage can feel completely different depending on their shape and what fills them.
For a single rectangular room the calculation is nothing more than length times width. What makes whole-home square footage genuinely useful — and genuinely fiddly to get right by hand — is that it is almost never one rectangle. Real floor plans are collections of rooms, hallways, closets and sometimes irregular shapes that all have to be measured and added separately, which is the exact problem this calculator exists to speed up.
Why the number on a real estate listing rarely matches a room-by-room sum
Square footage sounds like an objective figure, but different methods produce meaningfully different totals for the same building.
- Gross living area — the figure most residential listings use, typically measured to the exterior wall surfaces on above-ground, heated, finished levels — it usually runs larger than a sum of interior room measurements because it includes wall thickness and interior partitions.
- Interior (carpet) area — measured wall-to-wall inside each room, which is what a room-by-room calculation like this one naturally produces — closer to what a flooring or paint estimate actually needs.
- What typically gets excluded — unfinished basements, garages, and often outdoor space like porches and decks are commonly left out of a home's advertised square footage, even though they are very real usable area.
Measuring a real floor plan
A careful room-by-room measurement avoids the most common sources of error.
- 1Measure wall-to-wall inside each room — for a flooring or paint estimate this is the number that matters — not the exterior building footprint.
- 2Split irregular rooms into rectangles — an L-shaped room becomes two rectangular lines added together; the same approach handles bay windows, alcoves and closets treated as separate rooms.
- 3Decide deliberately whether to include hallways and closets — they count toward interior area but are easy to forget when walking room to room, and skipping them is the most common reason a manual total comes in low.
- 4Keep units consistent within each line — mixing feet and inches on the same line without converting first is the single most common source of a wildly wrong total.
Where a square footage total actually gets used
The same total feeds several very different downstream calculations, which is why getting it right matters beyond mere curiosity.
- Flooring, tile and paint estimates — material calculators start from a total area, then apply their own coverage rate and waste allowance on top.
- Real estate pricing — price per square foot is one of the most common ways buyers and agents compare homes, even though it ignores layout, condition and location.
- Rent and lease pricing — commercial and some residential leases are quoted per square foot per year, making an accurate total the basis of the whole rent calculation.
- HVAC and insulation sizing — contractors use total conditioned floor area as a starting input before adjusting for ceiling height, window area and climate.
What this assumes, and where it stops
Assumptions
- Each line is treated as a simple rectangle — length times width.
- All figures are inside (carpet) measurements unless you have specifically measured to the exterior walls.
Limitations
- Irregular rooms must be split into rectangles by hand before entering them; this does not solve for angled or curved walls directly.
- Does not distinguish finished from unfinished space, or above-grade from below-grade — a real estate listing figure may follow different rules than a plain room-by-room sum.
- Does not account for wall thickness, so a total measured room-by-room will typically read a little lower than a home's official exterior-wall listed square footage.
Common questions
Why is my calculated total lower than the square footage on the listing?
Listings commonly measure to the outside wall surfaces (gross living area), which includes the walls themselves and interior partitions. Measuring wall-to-wall inside each room — what this calculator assumes — leaves out that wall thickness, so the interior sum typically comes in a bit lower. Both are valid; they are just answering slightly different questions.
How do I handle an L-shaped or irregular room?
Split it into two or more rectangles on separate lines and let the calculator add them together — the same way a flooring installer or appraiser would measure it on site. A bay window, alcove or closet can be entered the same way, as its own line.
Should hallways and closets count toward the total?
For a flooring or paint estimate, yes — anything with floor to be covered belongs in the total. For comparing to a real estate listing, check which convention the listing uses, since some gross-living-area figures include them and some room-count-based estimates do not.
Formula and content last reviewed on .
Results are estimates for information only, not professional advice.
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