Calculate square footage for any room, floor, or irregular space. Add multiple rooms to get total house square footage. Also calculates paint needed, flooring materials, and cost estimates. Supports rectangle, circle, triangle, and L-shaped rooms. Free, instant, no sign-up.
Room area, paint, flooring & multi-room total
Square footage is one of the most practically useful measurements in everyday American life — from buying or renting a home to ordering flooring, calculating paint, determining HVAC capacity, or estimating property tax assessments. To measure a rectangular room, multiply length × width in feet. For a 15×12 foot bedroom: 15 × 12 = 180 square feet. For total house square footage, measure each room and add them together — but standard real estate practice (ANSI Z765) only includes heated/cooled finished living space above ground. Garages, unfinished basements, and attics are typically excluded from the official "above grade finished area."
Flooring calculations should always add 10% waste factor for rectangular rooms and up to 15% for rooms with angles, diagonal laying patterns, or natural stone/hardwood that requires matching grain. A 180 sq ft bedroom with 10% waste = 198 sq ft of material to order. Paint coverage: one gallon covers approximately 350–400 sq ft per coat of wall surface. For a 15×12 room with 9-foot ceilings: wall area = 2(15+12) × 9 = 486 sq ft. Subtract doors (~20 sq ft each) and windows (~15 sq ft each) for net paintable area. Two coats typically require 486/375 × 2 = ~2.6 gallons.
The average new single-family home in the US is 2,299 sq ft (2023 Census data). Median existing home: ~1,800 sq ft. A 2,000 sq ft home has roughly: 3 bedrooms (~400 sq ft each), 2 bathrooms (~80 sq ft each), living room (~300 sq ft), kitchen (~200 sq ft), dining room (~150 sq ft), and hallways/closets (~400 sq ft).
Flooring: luxury vinyl plank $2–$5/sq ft, hardwood $8–$15/sq ft, carpet $3–$8/sq ft, tile $5–$15/sq ft. Paint: ~$25–$50 per gallon (cover 350–400 sq ft). Home value: national median ~$420,000 ÷ 1,800 sq ft = ~$233/sq ft. New construction: $150–$250/sq ft depending on location and finishes.
A rough rule: 1 ton of cooling capacity per 400–600 sq ft (varies by climate, insulation, and ceiling height). A 2,000 sq ft home typically needs 3–4 tons of AC. An oversized unit short-cycles (turns on/off rapidly), reducing efficiency and failing to dehumidify properly. Have an HVAC technician perform a Manual J load calculation for accurate sizing.
Licensed appraisers follow ANSI Z765 standards: measure from exterior walls (including wall thickness). Only finished, heated/cooled above-grade space counts. Each floor is measured separately. Staircases count on the lower level only. Finished basements are listed separately as "below grade finished area" — not included in GLA (Gross Living Area).
Floor area is length times width for a rectangle, and the practical difficulty is that few real rooms are rectangles. The standard approach is decomposition: break an irregular plan into rectangles, triangles and circle segments, compute each, and add them — subtracting any permanent voids such as a stairwell or chimney breast. Material estimates then need a waste allowance on top, because tiles and boards are cut to fit: 10% is typical for a straight layout and 15% or more for diagonal patterns, where offcuts are less reusable.
Rectangle = length × widthTriangle = ½ × base × heightCircle = π × radius²Total = Σ shapes − voidsWith waste = Total × (1 + waste%)where:
Assumptions: Measure at the widest points and to the wall face. Flooring is usually sold by the box, so the final order rounds up to whole boxes — often more than the waste calculation alone suggests.
Decompose an L-shaped floor into two rectangles and order flooring for it.
Result315 sq ft of floor — 16 boxes to order
In square metres that is 29.26 m², since 1 sq ft is 0.092903 m². Keeping one spare box after installation is standard practice: dye lots vary between production runs, so a later repair using freshly bought material rarely matches.