Square Footage Calculator
This free square footage calculator turns room dimensions into the one number every other estimate needs. Add as many sections as you like, mix rectangles with triangles, circles, and trapezoids for L-shaped or irregular rooms, and subtract doors and windows so wall paint and drywall come out net of openings.
Square footage is the input to almost every material take-off. Get it right and your flooring boxes, paint gallons, tile, and drywall sheets all fall into place; get it wrong and every downstream count is off. The calculator also converts to square yards (for carpet), square meters (for metric plans and imported products), squares (for roofing and siding), and acres — and adds a waste factor so you can order in boxes, gallons, or sheets.
Built on plain plane geometry and the ANSI Z765 home-measurement method — no signup. When you have your total, hand it to the Flooring, Interior Paint, Tile, or Drywall calculator to turn area into materials.
Square Footage Calculator
Add up any number of rooms, walls, or lots — rectangles, triangles, circles, and trapezoids — and subtract doors and windows to get a net area. Converts instantly to square feet, square yards, square meters, and squares to feed every other calculator.
Measurement unit
Areas to measure
Ordering (optional)
Leave coverage blank to just get the area. Example: vinyl plank at 20 sq ft per box → enter 20, unit “boxes.”
Calculation Formulas
The base case for almost every room, wall, and lot. Multiply the two perpendicular dimensions in the same unit.
Example:
A 12 ft × 10 ft room = 120 sq ft.
For gable ends, corner cutoffs, and angled rooms. Height is the perpendicular distance from the base to the opposite point — not a sloped side.
Example:
A gable wall 24 ft wide and 6 ft tall at the peak = ½ × 24 × 6 = 72 sq ft.
For round patios, rugs, columns, and curved features. Enter the diameter; the radius is half of it.
Example:
A 10 ft round patio = π × 5² = 78.54 sq ft.
For four-sided spaces with two parallel sides of different length — pie-shaped lots, angled bump-outs, and tapered rooms.
Example:
Parallel sides of 12 ft and 8 ft, 10 ft apart = ½ × (12 + 8) × 10 = 100 sq ft.
Any L-shape, T-shape, or complex floor plan is split into rectangles, triangles, and circles, each measured separately, then summed. This is how appraisers and estimators handle non-rectangular rooms.
Example:
An L-shaped room = (16 × 12) + (8 × 6) = 192 + 48 = 240 sq ft.
For wall paint and drywall, subtract door and window areas from the gross wall area so you do not over-buy. Each opening is a rectangle removed from the total.
Example:
A 40 ft × 8 ft wall (320 sq ft) minus a 3 ft × 6.7 ft door (20 sq ft) = 300 sq ft to paint.
Carpet is sold by the square yard; metric plans and products use square meters. One square yard is a 3 ft × 3 ft = 9 sq ft tile.
Example:
300 sq ft ÷ 9 = 33.33 sq yd, or 300 ÷ 10.764 = 27.87 m².
Roofing and some siding are estimated by the "square" — 100 square feet of surface. Convert your area to squares before ordering shingle bundles or siding.
Example:
1,342 sq ft of roof ÷ 100 = 13.42 squares.
Real installs need extra material for cuts, breakage, and pattern matching. Apply a waste factor before converting to boxes, gallons, or sheets.
Example:
300 sq ft at 10% waste = 330 sq ft; at 20 sq ft per box that is ⌈330 ÷ 20⌉ = 17 boxes.
Standard Constants
| Constant | Value | Description |
|---|---|---|
| 1 square yard | 9 sq ft | A 3 ft × 3 ft square; carpet is priced and sold per square yard. |
| 1 square meter | 10.7639 sq ft | Metric area unit used on international plans and imported products. |
| 1 roofing square | 100 sq ft | The unit roofing and some siding are sold and estimated in. |
| 1 acre | 43,560 sq ft | Lot and land area; equals roughly 90% of a US football field. |
| 1 square foot | 144 sq in | 12 in × 12 in; small tile and sheet-good math sometimes runs in square inches. |
| Straight-lay flooring waste | 10% | Industry rule of thumb for plank/tile run square to the walls (NWFA / TCNA guidance). |
| Diagonal / pattern waste | 15% | Diagonal, herringbone, and large-format layouts cut more material. |
| Paint waste | 5–10% | Allowance for a second coat touch-up, texture, and roller loss. |
| π (pi) | 3.14159 | Used for every circular and round area. |
Note: All calculations include appropriate waste factors based on project complexity and material type. Results are estimates and should be verified by professionals before purchasing materials.
ANSI Z765 — Square Footage Method for Single-Family Residential(ANSI Z765-2021)
View StandardThe national standard most appraisers, builders, and MLS systems use to calculate the finished area of a house.
Key Requirements:
- •Measure to the exterior faces of the exterior walls.
- •Count only finished, heated living area; exclude garages and unfinished space.
- •Above-grade and below-grade (basement) finished areas are reported separately.
- •Areas with sloped ceilings count only where the ceiling is at least 5 ft high.
BOMA Floor Measurement Standards(BOMA 2017 / ANSI Z65.1)
View StandardThe commercial-real-estate standard for measuring office and other floor area (gross, rentable, and usable).
Key Requirements:
- •Distinguishes gross area, rentable area, and usable area.
- •Defines how shared/common areas are allocated to tenants.
- •Used for leasing math, not residential listings.
Appraisal Gross Living Area (GLA)(Fannie Mae UAD / URAR)
View StandardHow lenders and appraisers report living area on the standard appraisal form — closely aligned with ANSI Z765.
Key Requirements:
- •GLA is above-grade finished area only; basements are reported separately even when finished.
- •Consistent measurement method must be used across comparable sales.
- •Garage, porch, and unfinished attic are excluded from GLA.
NWFA Installation Guidelines — Waste Factor(NWFA)
View StandardWood-flooring association guidance on how much overage to add to measured area when ordering.
Key Requirements:
- •Add roughly 5% for waste on straightforward installs, more for complex rooms.
- •Diagonal and herringbone layouts require larger allowances.
- •Always order from the same lot/run to match color and milling.
TCNA Handbook — Tile Coverage(TCNA)
View StandardTile Council of North America guidance on coverage and waste when translating area into tile and setting materials.
Key Requirements:
- •Add 10% waste for standard layouts, 15%+ for diagonal or large-format tile.
- •Account for pattern repeats and cuts at walls and penetrations.
- •Coverage rates for thinset and grout follow tile size and joint width.
Standards Disclaimer: Standards and codes are subject to periodic updates. Always verify current requirements with local building authorities and professional engineers before beginning construction. Links provided are for reference only.
Listing Square Footage vs. Material Square Footage
Appraisal/MLS GLA vs. what you are actually covering
The number on a real-estate listing (ANSI/GLA, measured to exterior walls, finished area only) is not the number you order materials against. For flooring, tile, or paint you measure the real surface, including closets and minus cabinets, walls, or fixtures.
Regional Examples:
Basement & Below-Grade Area
How finished basements are counted
Most standards exclude below-grade space from above-grade living area even when finished, but it is reported separately and absolutely counts for flooring, paint, and drywall take-offs.
Regional Examples:
Sloped Ceilings & Attics
Knee walls and low headroom
For living-area reporting, only the portion of a sloped-ceiling room with at least 5 ft of headroom counts. For materials (flooring, insulation), you still cover the full floor or assembly.
Regional Examples:
Metric vs. Imperial Markets
Square meters on plans and products
Most of the world, and many imported tile and flooring products, are specified in square meters. Plans drawn in metric need conversion before they meet US-sold materials.
Regional Examples:
Wall Area vs. Floor Area
Paint and drywall measure the walls, not the floor
Flooring and ceilings use floor area (length × width). Paint and drywall use wall area (perimeter × height) minus door and window openings. The same room produces two very different square-footage numbers.
Regional Examples:
Before You Build
- •Contact your local building department for specific requirements
- •Verify frost line depths, wind zones, and seismic requirements for your area
- •Check if permits are required and schedule required inspections
- •Consult with a local contractor familiar with local codes
Plan disposal before you start
Smaller jobs still produce more debris than a few trash bags can hold. Check what's allowed in a dumpster and which disposal option fits the scope.
See disposal options →
Related Calculators
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Interior Paint Calculator
Instantly calculate interior paint gallons for walls, ceilings & trim—doors and windows subtracted automatically. Free, fast, no signup needed.
Tile Calculator
Calculate tiles, thin-set, grout (TCNA formula), membrane, leveling clips & EJ171 movement joints for floor, wall or shower. Free, no signup.
How to Use This Calculator
- Pick the unit your dimensions are in — feet, inches, yards, meters, or centimeters. Everything converts to square feet.
- For each room or wall, choose a shape (rectangle, triangle, circle, or trapezoid) and enter its dimensions. Use the quantity field for several identical sections.
- Add more sections with “Add area” to handle L-shapes and multi-room totals — each section is summed into the total.
- For wall paint or drywall, add the walls as rectangles, then use “Subtract opening” for each door and window so they come out of the total.
- Optional: set a waste/overage factor (10% is typical for flooring and tile) and a coverage rate (sq ft per box, gallon, or sheet) to get the number of units to buy.
- Click Calculate to see the total in square feet, square yards, square meters, and squares, plus a per-section breakdown.
- Copy or save the result, then open the Flooring, Paint, Tile, or Drywall calculator to convert your area into materials.
Floor Area vs. Wall Area
The same room gives two different square-footage numbers depending on what you are covering. Flooring and ceilings use the floor area — length × width. Paint and drywall use the wall area — the room perimeter times the wall height, minus the doors and windows. To get wall area here, add each wall as a rectangle (its length × the ceiling height) and then subtract each opening. For listing or appraisal square footage, ANSI Z765 measures finished living area to the exterior wall faces and reports basements separately — that figure is for real-estate purposes, not for ordering materials, where you measure the actual surface you are covering and add waste.
Frequently Asked Questions
How do I calculate the square footage of a room?
For a rectangular room, multiply the length by the width in the same unit — a 12 ft by 10 ft room is 120 square feet. For an L-shaped or irregular room, split it into rectangles (and triangles or circles for angled or curved areas), calculate each piece separately, and add them together. This calculator does that for you: add a section per shape, enter its dimensions, and it sums the total. If you have measurements in inches, switch the unit to inches and it converts to square feet automatically.
How do I find square footage for an irregular or L-shaped room?
Break the shape into simple pieces. An L-shaped room is two rectangles; a room with an angled wall is a rectangle plus a triangle; a curved bay is a rectangle plus part of a circle. Measure each piece, calculate its area, and add them up. Use the “Add area” button to stack as many sections as you need — rectangles, triangles, circles, and trapezoids — and the calculator totals them. This is the same decomposition method appraisers and estimators use for non-rectangular floor plans.
How do I convert square feet to square yards or square meters?
To convert square feet to square yards, divide by 9 (a square yard is a 3 ft by 3 ft tile, or 9 sq ft) — carpet is sold this way. To convert square feet to square meters, divide by 10.764. Going the other way, multiply square meters by 10.764 to get square feet, so a 25 m² product is about 269 sq ft. The calculator shows all of these conversions at once, plus squares (100 sq ft, used for roofing and siding) and acres (43,560 sq ft).
Should I subtract doors and windows from square footage?
It depends on what you are covering. For flooring, you do not subtract anything — you cover the whole floor. For wall paint and drywall, you do subtract doors and windows, because you are not finishing those areas. To get a net wall area here, add each wall as a rectangle (wall length times ceiling height) using “Add area,” then add each door and window with “Subtract opening.” The total comes out net of the openings, so you don't over-buy paint or drywall.
How much waste should I add to my square footage when buying materials?
The measured area is the starting point; you order more to cover cuts, breakage, and pattern matching. Industry rules of thumb: about 10% for straight-lay flooring and tile, 15% or more for diagonal, herringbone, and large-format layouts, and 5–10% for paint. Set the waste factor in the calculator and it shows the area to actually purchase, then converts that to boxes, gallons, or sheets if you enter a coverage rate. Always order flooring and tile from the same lot so color and milling match.
What is the difference between listing square footage and the area I measure for materials?
Listing or appraisal square footage follows the ANSI Z765 standard: it measures finished, heated living area to the exterior faces of the exterior walls, excludes garages and unfinished space, and reports finished basements separately. That number is for real estate, not material take-offs. For ordering flooring, paint, or tile, you measure the actual surface you are covering — the real room dimensions, including closets, minus cabinets or fixtures — which is usually different from the GLA on a listing.
Why doesn't this calculator give me a price or material count by itself?
Square footage is the upstream measurement — it tells you the area, and area alone doesn't fix the number of boxes, gallons, or sheets without a product's coverage rate and your waste factor. Enter a coverage rate and the calculator will convert area into units to buy; for full material take-offs with the right waste and product assumptions, hand your total to the Flooring, Interior Paint, Tile, or Drywall calculator. We keep every calculator pricing-free because material prices drift too fast to keep accurate, so you get quantities, not dollar figures.