Square Footage CalculatorMeasure any room, floor or whole house in square feet and square metres, including L-shaped, triangular, circular and irregular spaces, the way appraisers do
Add each room, pick its shape and type in the measurements (12’6″ works, so does 3.8 m). The calculator sketches your floor plan to scale, totals your finished living area under the ANSI Z765 rules lenders use, converts to m², square yards and acres, and works out flooring, paint and concrete for the space.
By Manzoor Ahmad · 13+ years of web development & SEO experienceUpdated October 21, 2026 · reflects UAD 3.6 terminology
tip → Type feet and inches as 12’6, 12 6 or 12.5. Measure wall to wall, and treat odd rooms as two shapes.
Add a space:
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Estimates for the area you choose below. Prices are placeholders; use your local quotes.
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How to calculate square footage
For a rectangular room, multiply the length by the width. A room 12 feet long and 10 feet wide is 120 square feet.
Square feet = length (ft) × width (ft)
If you measured in inches, divide the result by 144. In metres, multiply square metres by 10.7639 to get square feet. For a whole house, split it into rectangles and simple shapes, find each area, and add them up, counting only the spaces that qualify as finished living area.
12'6" × 10'3" = 12.5 × 10.25 = 128.1 sq ft
Always convert inches to decimal feet before multiplying (6 inches = 0.5 ft, 3 inches = 0.25 ft). Multiplying 12.6 × 10.3 by mistake gives 129.8, which is off by almost 2 sq ft per room.
Worked example: the sample house
Square footage formulas for every shape
Real rooms are rarely perfect rectangles. Break any space into these five shapes and add the pieces together.
L × W(L₁ × W₁) + (L₂ × W₂)base × height ÷ 2π × (diameter ÷ 2)²(top + bottom) ÷ 2 × heightA half-circle is half the circle formula; a bay window is usually a trapezoid; a closet under a staircase is often a triangle. For land and lots, which are measured in acres, use the acreage calculator, which handles irregular parcels.
How to measure the square footage of a house (ANSI Z765)
Fannie Mae and Freddie Mac require appraisers to measure using the ANSI Z765-2021 standard. If you want your number to match an appraisal, follow the same rules.
Any level that is partly or fully below ground is reported separately as basement area, even if it’s beautifully finished.
Finished areas need ceilings of at least 7 ft. Under sloped ceilings, at least half the room must reach 7 ft, and anything under 5 ft is excluded.
Measure to the nearest inch or tenth of a foot along exterior walls, and report the total to the nearest whole square foot.
Two-story foyers and other openings to the floor below are excluded from the upper floor’s area. Stairs count on the level they descend from.
Spaces must be finished, heated and connected to the main house. A finished room over a detached garage is reported separately.
Under UAD 3.6, mandatory from November 2, 2026, “gross living area” becomes “finished above-grade area” on appraisal reports.
| Space | Counts as finished above-grade area? | How it’s reported |
|---|---|---|
| Bedrooms, kitchen, living areas, baths | Yes | Finished above-grade area |
| Hallways, closets, interior stairs | Yes | Included with the floor they’re on |
| Finished basement (even a walk-out) | No | Finished below-grade area |
| Attached garage | No | Garage area |
| Unheated sunroom, porch, deck, patio | No | Listed separately as an amenity |
| Attic under 5 ft, crawl space | No | Not counted |
That’s why a listing, a tax record and an appraisal can disagree. Listings sometimes include finished basements, tax assessors may use exterior footprints, and appraisers follow ANSI. If your county has the size wrong, it can affect your bill; check it against the property tax calculator and appeal if needed.
Measuring a room in five minutes
- Sketch it firstDraw a rough outline on paper and split any odd shape into rectangles, triangles or half-circles.
- Measure wall to wallRun the tape along the floor at the baseboards, keep it straight, and record feet and inches.
- Measure every pieceFor each shape, take the two or three dimensions its formula needs, and label them on your sketch.
- Convert and multiplyTurn inches into decimal feet, then multiply. Or type the numbers above and let the calculator do it.
- Add, then sortTotal the pieces, then separate living space from basement, garage and outdoor space.
- Buy a little extraFor flooring and tile, add 5%–15% for cuts and waste; more for diagonal or herringbone layouts.
Square feet conversion chart
| Square feet | Square metres | Square yards | Acres |
|---|---|---|---|
| 100 sq ft | 9.29 m² | 11.1 sq yd | 0.0023 ac |
| 500 sq ft | 46.45 m² | 55.6 sq yd | 0.0115 ac |
| 1,000 sq ft | 92.90 m² | 111.1 sq yd | 0.0230 ac |
| 2,183 sq ft (median new US home) | 202.81 m² | 242.6 sq yd | 0.0501 ac |
| 3,000 sq ft | 278.71 m² | 333.3 sq yd | 0.0689 ac |
| 43,560 sq ft | 4,046.86 m² | 4,840 sq yd | 1 ac |
1 square metre = 10.7639 square feet, 1 square yard = 9 square feet and 1 acre = 43,560 square feet. Carpet is often priced per square yard, so divide square feet by 9 to compare quotes.
What your square footage is used for
Square footage sits behind almost every number in a home’s life. The median new single-family home completed in late 2025 had 2,183 sq ft of floor area (Census data, NAHB analysis), and that figure drives price, cost and value comparisons:
| Use | How square footage matters | Tool |
|---|---|---|
| Building | Builders quote cost per square foot of finished living area. | Cost to build a house |
| Buying & selling | Price per square foot is the fastest way to compare homes; agents price listings with it. | Commission · Seller net |
| Property tax | Assessors use size to value your home; a wrong record can mean a higher bill. | Property tax |
| Renting | Rent per square foot shows whether a unit is fairly priced against the neighborhood. | Rent affordability · Prorated rent |
| Investing | Investors compare price and rent per square foot across deals before running returns. | Rental property · Rental yield |
| Renovating | Flooring, paint, insulation and HVAC sizing all start with area. | HELOC · House flip |
Mistakes that throw off a square footage number
- Multiplying feet and inches as decimals10’6″ is 10.5 ft, not 10.6. It’s the most common error and it compounds across a whole house.
- Counting the basement as living areaAppraisers report it separately; including it inflates price-per-square-foot comparisons.
- Measuring furniture, not wallsMeasure along the floor at the walls, and include closets in the room’s area.
- Double-counting overlapsWhen you split an L-shaped room, make sure the two rectangles don’t overlap.
- Forgetting wasteOrdering exactly the floor area leaves you short; buy extra for cuts, pattern matching and future repairs.
- Trusting the listingListing sizes aren’t always ANSI-measured. If size affects your offer, measure it yourself or check the appraisal.
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This is part of the complete property and real estate calculators collection, covering buying, selling, renting, investing, home loans and land.
Square footage FAQ
How do I calculate square footage of a room?
Multiply the room’s length by its width in feet. A 12 × 15 ft room is 180 sq ft. For odd shapes, split the room into rectangles, triangles or circles and add the areas together.
How do I calculate square footage with feet and inches?
Convert inches to decimal feet by dividing by 12 (6 in = 0.5 ft), then multiply. 12’6″ × 10’3″ = 12.5 × 10.25 = 128.1 sq ft.
How do I find the square footage of an L-shaped room?
Divide it into two rectangles that don’t overlap, calculate each one’s length × width, and add them. A 14 × 11 ft section plus a 6 × 4 ft section is 154 + 24 = 178 sq ft.
How do I calculate the square footage of a house?
Measure the exterior of each above-ground level, calculate each floor’s area, and add them. Under ANSI Z765, report basements, garages and areas with ceilings under 5 ft separately.
Does a finished basement count as square footage?
Not as finished above-grade area. Appraisers report it separately as below-grade finished area, though many listings mention it alongside the main living area.
Does a garage count in square footage?
No. Garages are reported separately and don’t count toward living area, even when attached.
How many square feet are in a square metre?
10.7639. To convert square metres to square feet, multiply by 10.7639; to go the other way, divide.
How many square feet are in an acre?
43,560 square feet, or about 4,047 square metres.
How do I calculate the square footage of a circle or triangle?
Circle: π × radius². Triangle: base × height ÷ 2. A 10 ft-diameter round room is about 78.5 sq ft; a triangle with a 10 ft base and 8 ft height is 40 sq ft.
How much extra flooring should I buy?
Usually 5%–10% for straight layouts and 10%–15% or more for diagonal, herringbone or patterned installations, plus any leftover boxes you want for repairs.
What is the average size of a new home?
The median new single-family home completed in the fourth quarter of 2025 had 2,183 sq ft of floor area, according to Census data analyzed by NAHB.
Is this square footage calculator free?
Yes. It’s free, needs no sign-up and runs entirely in your browser; your rooms and measurements aren’t sent anywhere.
Manzoor Ahmad
13+ years of web development & SEO experience · Founder, DexoCalc
Manzoor builds and maintains every DexoCalc calculator, including the full property and real estate collection this tool completes. It measures five shapes in feet-and-inches or metres, sketches the plan to scale, sorts each space by the ANSI Z765 categories appraisers use, and carries the result into material and price estimates.
Sources
- McKissock Learning — Understanding gross living area and ANSI Z765-2021
- McKissock Learning — Fannie Mae and Freddie Mac adopt the ANSI measuring standard
- NAHB Eye on Housing — New single-family home size, Q4 2025 (Census data)
- National Association of Realtors — Why square footage disputes arise
- NIST — SI units of area and conversion factors
This calculator is for planning and estimating. Official square footage for an appraisal, listing or legal document should come from a qualified measurer following ANSI Z765 or your local standard. Material quantities are estimates; confirm coverage on the product label.