Square Footage Calculator
Floor area in square feet from length and width, with circular and irregular-shape variants
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What this calculator computes
Square-footage calculation is the foundation of every flooring, painting, roofing, and real-estate area estimate, with applications spanning materials ordering, cost estimation, and listing-area documentation. The calculator handles the basic rectangular case (area = length × width), the circular case (area = π × radius²), the triangular case (area = 0.5 × base × height), and irregular-shape decomposition where a complex floor plan is broken into rectangular and triangular pieces and the individual areas are summed. The output appears in square feet (the standard US unit), square yards (used in some flooring contexts and historical real-estate documents), and square metres (the standard international unit and the figure required for any cross-border property comparison). For materials ordering, the calculator adds a recommended waste factor — typically 10% for tile and hardwood flooring with simple cuts, 15% for diagonal patterns and complex layouts, 20% for natural-stone work where matching grain and minimising visible cuts demands extra material. For real-estate documentation, the gross-vs-net distinction matters: gross square footage includes exterior wall thickness while net (or "usable") square footage measures only the interior walkable area, with the typical 5–10% gap depending on construction type. The ANSI Z765 standard defines residential single-family square-footage measurement protocols, with specific rules about garage inclusion, finished-vs-unfinished basement treatment, and second-floor area calculation that listings and appraisals follow.
Calculator
The formula
Formula
A = L × W (rectangular); A = π × r² (circular); A = 0.5 × b × h (triangular)
Worked example
When to use this calculator
Use this calculator at the materials-ordering and cost-estimation stage of any project that involves area-based purchasing: flooring (tile, hardwood, vinyl, carpet), painting (interior wall paint at typical 350 sq ft per gallon coverage), roofing (shingles by the square, where 1 square = 100 sq ft of roof), and concrete (where the square-foot area combined with thickness gives cubic-yard volume). Real-estate professionals use it for listing area calculation; appraisers use it for gross-vs-net documentation; contractors use it for bid-quantity validation. The calculator handles standard rectangular and circular shapes; for irregular floor plans, decompose the shape into rectangles and triangles, calculate each piece, and sum. The calculator does not substitute for the appraiser-grade measurement protocols (ANSI Z765 for residential single-family) that real-estate listings require for legal-documentation purposes, where exterior measurement, wall-thickness rules, and inclusion of attached garages all follow specific conventions.
Common input mistakes
- Mixing units in the area calculation. A 12 ft × 8 in dimension cannot be multiplied directly to produce square feet — the inches must be converted to feet (8 in = 0.667 ft) before multiplying. Failing to convert produces a result 12× larger than the actual area. The same trap applies when mixing yards and feet, or metres and centimetres.
- Forgetting the waste factor for materials ordering. Real-world flooring, tile, and roofing installations lose material to cut-and-fit waste, pattern matching, and end-of-roll remainders. A 312 sq ft net area typically needs 343–360 sq ft ordered (10–15% waste) to finish cleanly without a costly second materials run. Tile work with diagonal patterns or natural-stone matching may require 20% waste or more.
Frequently asked questions
How do I calculate square footage of a room?
Multiply the length by the width for a rectangular room. A 12 ft × 16 ft room is 192 square feet. For non-rectangular shapes, decompose the floor plan into rectangles and triangles, calculate each piece's area, and sum the totals. For circular or curved-shape rooms, use the circular-area formula A = π × r² with the radius measured from the centre to the wall.
How much waste should I add for flooring?
Standard rectangular layouts on hardwood, vinyl, or carpet need 10% waste for cut-and-fit losses; diagonal-pattern layouts and complex floor plans need 15%; natural-stone tile work or patterns requiring grain matching may need 20% or more. The waste factor covers cuts at room boundaries, end-of-row remainders that do not fit anywhere else, and the unavoidable losses from blade kerf and breakage during installation. Always check the manufacturer's specific recommendation for the chosen product.
How do I convert square feet to square metres?
One square foot equals 0.0929 square metres, so multiply the sq ft figure by 0.0929 to get sq m. A 1500 sq ft house converts to 139.4 sq m; a 200 sq ft room converts to 18.6 sq m. The conversion is exact and traces back to the foot-to-metre relationship: 1 ft = 0.3048 m, so 1 sq ft = 0.3048² = 0.0929 sq m.
What is gross vs net square footage in real estate?
Gross square footage measures the total area enclosed by the exterior walls, including the wall thickness itself. Net (or usable, or "carpet area") square footage measures only the interior walkable area, excluding wall thickness, structural columns, and sometimes utility chases. The two typically differ by 5–10% depending on construction type, with stick-frame residential construction at the lower end and concrete-and-block construction at the higher end. Real-estate listings sometimes use one and sometimes the other; ANSI Z765 specifies gross for US residential single-family.
How much paint do I need for a room?
Calculate the wall area (perimeter × ceiling height) and subtract the area of doors and windows (typically 21 sq ft per door, 15 sq ft per window). Then divide by the paint's coverage rating, typically 350 sq ft per gallon for the first coat and 400 sq ft per gallon for the second coat over previously painted surfaces. A 12 ft × 16 ft room with 8 ft ceilings, two doors, and two windows has wall area (12+16) × 2 × 8 − (2 × 21 + 2 × 15) = 448 − 72 = 376 sq ft, requiring just over 1 gallon for one coat or 2 gallons for two coats with comfortable margin.