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.
Painters and drywallers can skip the wall-by-wall arithmetic: add a room or shed section, type length, width, and wall height once, and the calculator unwraps the box into all four walls (perimeter × height), the ceiling, an optional floor, and gable ends for a shed, garage, or vaulted ceiling — then knocks out the doors and windows. The result separates wall area from ceiling area, because they are separate line items on a paint job.
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. Painting or drywalling? Enter a room or shed as length × width × wall height and it unwraps into all four walls plus the ceiling, minus the doors and windows — no adding one rectangle per wall. Mix in rectangles, triangles, circles, and trapezoids for odd shapes, and convert instantly to square feet, square yards, square meters, and squares.
Measurement unit
Enter every dimension in this unit — the result converts to square feet.
Areas to measure
Painting or drywalling? Use “Add room or shed” to enter length × width × wall height once and get all four walls plus the ceiling. For floors and lots, add a flat shape per area and use “Subtract” for cutouts.
Ordering (optional)
Add a waste factor and a coverage rate to turn area into the number of boxes, gallons, or sheets to buy.
Leave coverage blank to just get the area. Example: vinyl plank at 20 sq ft per box → enter 20, unit “boxes.”
Measuring area the reliable way
The math is simple once the space is broken down right. Three things trip people up: splitting an irregular room into simple shapes you can actually measure, deciding what to subtract (doors and windows come off wall paint and drywall, but not off flooring), and converting square feet into the unit each trade orders in— square yards, squares, or acres.
The shape-breakdown diagram is why you never measure an odd room directly. The calculator splits it into simple shapes it knows — rectangle, triangle, circle, trapezoid — finds each area, and adds them, so an L-shape is two rectangles. Breaking the shape down is what makes an irregular room come out right.
The add-and-subtract diagram is why the calculator separates gross and net area. Add sections build up the surface and subtract sections remove doors, windows, and cutouts, so wall paint and drywall want the net while flooring usually wants the gross. Knowing which you need is why the same room gives two valid numbers.
The unit-conversion diagram is why square feet is the hub of the estimate. From square feet you convert to whatever the material is sold in — square yards, squares, or acres — so the calculator computes area once and converts. Add your waste factor before ordering, because the conversion does not.
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
Have your square footage? Drop it into a project calculator
These calculators take this number as an input — pick your project and carry the figure straight over.
Concrete & Rebar
Flooring
Foundations & Drainage
HVAC & Ventilation
Insulation & Climate
Landscaping
Masonry, Stucco & Hardscape
Paint & Wallpaper
Roofing & Gutters
Tile, Grout & Mortar
Share this calculator with your customers
Run a contractor site, supply store, or blog? Drop this free square footage calculator straight onto your own page so your visitors can estimate materials without leaving. No signup, works on any website — just copy and paste.
Want to Learn More?
How to measure walls, ceilings, and trim for accurate paint estimates. Covers L-shaped rooms, stairwells, angled ceilings, and window and door deductions.
Read the How to Measure Your Room & Calculate Square Footage
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
Flooring Calculator
Instantly calculate flooring sq ft, boxes & cost with waste factor for tile, hardwood, laminate, LVP & carpet. Free, accurate, no signup required.
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.
Sod Calculator
Free sod calculator: square feet, slabs, rolls, and pallets for your lawn — with editable, region-aware pallet coverage plus topsoil and starter fertilizer.
Grass Seed Calculator
Free grass seed calculator with extension-cited rates by species for new lawns, overseeding & winter overseed. Get pounds to buy, bags, and starter fertilizer.
Home Addition Cost Calculator
Free home addition cost calculator and estimator — instant low/likely/high price ranges by type, foundation, finish, and region, with soft costs itemized.
How to Use This Calculator
- Pick the unit your dimensions are in — feet, inches, yards, meters, or centimeters. Everything converts to square feet.
- Painting, drywalling, or finishing a shed? Click “Add room or shed” and enter length × width × wall height once — the calculator unwraps the room into all four walls (perimeter × height) plus the ceiling, so you never add one rectangle per wall.
- On a room section, tick Ceiling and/or Floor for the surfaces you are covering, enter how many doors and windows to knock out, and add a gable/peak rise for a shed, garage, or vaulted ceiling.
- For floors, lots, and odd shapes, use “Add area” instead and choose a flat shape (rectangle, triangle, circle, or trapezoid). Use the quantity field for several identical sections.
- Add as many sections as you need to handle L-shapes and multi-room totals — each one is summed into the total. Use “Subtract opening” for odd-sized openings like a slider or garage door.
- 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 uses the floor area — length × width. Paint, drywall, and wallpaper use the wall area — the room perimeter times the wall height, minus the doors and windows. The “Add room or shed” section does that second calculation for you: enter length, width, and wall height once and it returns 2 × (length + width) × height for the walls, adds the ceiling if you want it, and subtracts a nominal 20 sq ft per door and 12 sq ft per window. It is why a long, narrow room needs more paint than a square room with the same floor area — a 20 ft × 6 ft room and a 11 ft × 11 ft room are both about 120 sq ft of floor, but the narrow one has 52 ft of perimeter against 44 ft, roughly 70 more sq ft of wall at 9 ft ceilings. 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. The shape breakdown diagram shows splitting into simple shapes. Planning a room addition? The home addition calculator sizes the whole build from the same footprint.
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). The unit conversion diagram shows the conversion factors.
Why isn't a room's square footage length × width × height?
Because that formula gives volume, not area. A 20 ft × 10 ft room with 10 ft ceilings is 2,000 CUBIC feet — the air inside it — which is the number you'd want for sizing an HVAC unit or a dehumidifier, not for buying paint or drywall. Square footage measures flat surfaces, one at a time. That same room has 200 sq ft of floor (20 × 10), 200 sq ft of ceiling, and 600 sq ft of wall (the 60 ft perimeter × the 10 ft height) — 1,000 sq ft total if you count all six faces of the box. Painters quote the 600, or 800 with the ceiling. If you actually want cubic feet, use the cubic yards calculator, which reports both cubic feet and cubic yards.
How do I calculate the square footage of walls for painting?
Wall area is the room perimeter times the wall height: 2 × (length + width) × ceiling height. A 12 ft × 10 ft room with 9 ft ceilings has a 44 ft perimeter, so 44 × 9 = 396 sq ft of wall before openings. Click “Add room or shed,” enter the length, width, and wall height once, and the calculator does that for you — then tick Ceiling to add the 120 sq ft lid, and enter how many doors and windows to knock out. It reports wall area and ceiling area separately, because they are separate line items on a paint job: different sheens, usually different colors. Note that floor area does not predict wall area — a long, narrow room has far more wall than a square room with the same square footage.
How do I figure the square footage of a shed or a room with a vaulted ceiling?
A gable-roofed shed is four walls plus two triangular gable ends. Add a room section, enter the length, width, and side-wall height, untick Ceiling if the rafters are open, and enter the gable rise — the vertical distance from the top of the wall to the peak. The calculator adds both gable triangles (each ½ × width × rise, so width × rise for the pair). A 12 ft × 8 ft shed with 7 ft walls and a 2 ft rise comes out to 280 sq ft of wall plus 16 sq ft of gable. The same approach handles a vaulted or cathedral ceiling in a house: side walls at wall height, plus the gable rise for the peaked end walls.
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. A room section does it by count: enter the number of doors and windows and it removes a nominal 20 sq ft per door (3 ft × 6 ft 8 in, the IRC R311.2 egress leaf) and 12 sq ft per window (3 ft × 4 ft). For an odd-sized opening — a 6-ft slider, a garage door, a fireplace surround — leave those at 0 and add a “Subtract opening” section with the real measurements. Many painters skip small openings entirely and let them cover the cut-in waste; subtract them if you are ordering drywall sheets. The add-and-subtract diagram shows net area for paint and 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.