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Calculate area for rooms, properties, flooring, and more. Convert between sq ft, sq m, acres, and hectares with accurate formulas.
L × W
Rectangle formula
π × r²
Circle formula
43,560
Sq ft per acre
10.764
Sq ft per sq m
Free online square footage calculator — compute area for rectangles, circles, triangles, and trapezoids with AI-powered insights.
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Square footage measures the two-dimensional area of a surface in square feet (sq ft or ft²). One square foot equals a flat area measuring 1 foot by 1 foot (12 inches × 12 inches = 144 square inches). It's the primary unit for measuring floor space, room size, property area, and material quantities in the United States.
Accurate square footage calculation is essential for real estate valuations (price per square foot is the standard comparison metric), construction material estimation (flooring, paint, tiles), HVAC sizing (BTU requirements), rental pricing, and property tax assessments. An error of even 5% in a 2,000 sq ft home represents 100 sq ft — potentially affecting property value by thousands of dollars.
Most rooms are rectangular, making area calculation straightforward (length × width). However, real homes have irregular shapes — L-shaped rooms, bay windows, angled walls, closets, and built-in features. The key technique is to divide complex shapes into simple rectangles, calculate each area separately, and sum them. For irregularly shaped lots, surveyors use the coordinate method or divide the lot into triangles.
Rectangle:
Area = Length × Width
Example: 15 ft × 12 ft = 180 sq ft
Square:
Area = Side × Side = Side²
Example: 10 ft × 10 ft = 100 sq ft
L-Shaped Room:
Split into two rectangles
Area = (L₁ × W₁) + (L₂ × W₂)
Example: (15 × 10) + (8 × 6)
= 150 + 48 = 198 sq ft
Perimeter:
P = 2(L + W)
Example: 2(15 + 12) = 54 ftMost rooms are rectangular. For L-shapes, T-shapes, or U-shapes, break into rectangles and add areas.
Triangle:
Area = ½ × Base × Height
Example: ½ × 20 ft × 15 ft = 150 sq ft
Right Triangle:
Area = ½ × Leg₁ × Leg₂
Example: ½ × 8 × 6 = 24 sq ft
Hypotenuse = √(8² + 6²) = 10 ft
Trapezoid:
Area = ½ × (Base₁ + Base₂) × Height
Example: ½ × (20 + 14) × 10
= ½ × 34 × 10 = 170 sq ft
Heron's Formula (any triangle):
s = (a + b + c) / 2 (semi-perimeter)
Area = √(s(s−a)(s−b)(s−c))Irregular lots often use triangles. Heron's formula works when you know all three sides but not the height.
Circle: Area = π × r² Example: r = 8 ft Area = 3.14159 × 64 = 201.06 sq ft Semi-circle: Area = ½ × π × r² Example: r = 6 ft Area = ½ × 3.14159 × 36 = 56.55 sq ft Ellipse: Area = π × a × b (a = semi-major, b = semi-minor axis) Example: a = 12 ft, b = 8 ft Area = 3.14159 × 12 × 8 = 301.59 sq ft Circumference = 2 × π × r Example: 2 × 3.14159 × 8 = 50.27 ft
| From | To | Multiply By | Example |
|---|---|---|---|
| Square feet | Square meters | 0.0929 | 1,000 sq ft = 92.9 sq m |
| Square meters | Square feet | 10.764 | 100 sq m = 1,076.4 sq ft |
| Square feet | Square yards | 0.1111 | 2,000 sq ft = 222.2 sq yd |
| Square feet | Acres | 1/43,560 | 10,890 sq ft = 0.25 acres |
| Acres | Square feet | 43,560 | 1 acre = 43,560 sq ft |
| Acres | Hectares | 0.4047 | 5 acres = 2.02 ha |
| Space | Average Size (sq ft) | Range | Typical Dimensions |
|---|---|---|---|
| US home (median) | 2,261 | 1,000–5,000+ | varies |
| Master bedroom | 224 | 200–350 | 14 × 16 |
| Standard bedroom | 132 | 100–200 | 11 × 12 |
| Living room | 330 | 200–500 | 16 × 20 |
| Kitchen | 160 | 100–300 | 12 × 13 |
| Full bathroom | 75 | 40–100 | 8 × 9 |
| City | Avg $/sq ft | Median Home Price | Median Home Size |
|---|---|---|---|
| San Francisco, CA | $750+ | $1,350,000 | 1,800 sq ft |
| New York City, NY | $650+ | $750,000 | 1,150 sq ft |
| Los Angeles, CA | $550 | $925,000 | 1,700 sq ft |
| Miami, FL | $400 | $550,000 | 1,400 sq ft |
| Austin, TX | $280 | $475,000 | 1,700 sq ft |
| Chicago, IL | $250 | $325,000 | 1,300 sq ft |
Egyptian 'rope-stretchers' (harpedonaptai) used knotted ropes to re-measure field boundaries after annual Nile floods. They divided land into rectangular and triangular plots, calculating area for taxation purposes. The cubit (forearm length) was their primary linear measure.
Euclid formalized geometric area formulas in his 13-book treatise. Propositions in Book I proved the area of a parallelogram equals base × height, and triangles are half that. These formulas remain essentially unchanged in modern square footage calculations.
Edmund Gunter invented the 66-foot surveyor's chain (80 links). This standardized land measurement: 10 square chains = 1 acre. The chain system was used for centuries in English-speaking countries and influenced the US rectangular survey system that divided the American West.
Congress established the rectangular survey system to divide western territories into 6-mile × 6-mile townships, each containing 36 one-square-mile (640-acre) sections. This grid system, still visible in satellite imagery, standardized American land measurement and property descriptions.
US Census Bureau — Characteristics of New Housing
The median new single-family home size peaked at 2,386 sq ft in 2015, declining slightly to 2,261 sq ft by 2022. Average home sizes have grown 62% since 1973 (1,525 sq ft) while household sizes have shrunk from 3.01 to 2.53 persons — more space per person than ever.
NAHB — Cost of Constructing a Home
The National Association of Home Builders reports average construction cost of $150-$200/sq ft nationally (2023), ranging from $100/sq ft in rural South to $400+/sq ft in coastal cities. Land, labor, and materials account for roughly equal thirds. Finishing quality can double per-sq-ft costs.
BOMA — Office Space Standards
The Building Owners and Managers Association (BOMA) standard defines rentable square footage, usable square footage, and common area factors. The 'load factor' (typically 15-25%) represents shared spaces (lobbies, corridors) added to usable space. A 1,000 sq ft usable office may have 1,200 sq ft rentable.
ANSI Z765 — Measuring Living Area
Square footage in the listing is always accurate.
Studies show 30-40% of home listings have square footage errors of 5% or more. Appraisers, tax records, and agents often use different measurement standards (ANSI Z765 vs. local rules). Some include finished basements; others don't. Always verify with your own measurement or professional appraisal.
Price per square foot is the best way to compare homes.
Price per square foot is useful but ignores critical factors: location, lot size, condition, finishes, layout efficiency, basement, garage, outdoor spaces, and school district. A 2,000 sq ft home with premium finishes in a good neighborhood can be worth far more than a 3,000 sq ft home in a lesser location.
Finished basements count toward square footage.
Under ANSI Z765 (the standard for real estate), finished basements are NOT included in above-grade living area, even if fully finished with bedrooms and bathrooms. They should be listed separately. However, some local MLS rules differ, and tax assessors may include below-grade space in their calculations.
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Circular areas appear in patios, pools, round rooms, and curved landscape features. Measure the diameter and divide by 2 for radius.
Strategy: Break into simple shapes
1. Identify rectangles, triangles, circles
2. Measure each section independently
3. Sum all areas (add protruding sections)
4. Subtract cutouts (alcoves, columns)
Example: Room with bay window
Main rectangle: 20 × 15 = 300 sq ft
Bay window (trapezoid):
½ × (6 + 4) × 3 = 15 sq ft
Closet alcove: 4 × 3 = 12 sq ft
Total = 300 + 15 + 12 = 327 sq ft
For irregular lots:
Use GPS coordinates or survey data
Apply Shoelace formula:
A = ½|Σ(xᵢyᵢ₊₁ − xᵢ₊₁yᵢ)|The Shoelace/Gauss formula calculates area from coordinates — surveyors use GPS points to compute lot areas precisely.
| Hectares | Acres | 2.471 | 1 ha = 2.471 acres |
| Square inches | Square feet | 1/144 | 1,440 sq in = 10 sq ft |
| Square feet | Square centimeters | 929.03 | 1 sq ft = 929.03 sq cm |
| Square miles | Acres | 640 | 1 sq mi = 640 acres |
| Half bath |
| 25 |
| 18–35 |
| 5 × 5 |
| 2-car garage | 400 | 350–600 | 20 × 20 |
| Apartment (1-BR) | 714 | 550–900 | varies |
| Apartment (2-BR) | 1,006 | 800–1,200 | varies |
Source: US Census Bureau, NAHB, and RECS survey data. Values represent national averages; regional variation is significant.
| Phoenix, AZ | $260 | $435,000 | 1,700 sq ft |
| Atlanta, GA | $220 | $385,000 | 1,750 sq ft |
| Houston, TX | $175 | $310,000 | 1,800 sq ft |
| Indianapolis, IN | $140 | $260,000 | 1,850 sq ft |
The American National Standards Institute published ANSI Z765, standardizing how to measure living area in single-family homes. This defined 'finished above-grade' space — basements, garages, and unfinished areas are excluded from square footage calculations used in real estate listings.
Laser distance measurers and smartphones with LiDAR sensors (iPhone Pro) can now calculate room dimensions and square footage with sub-inch accuracy in seconds. 3D scanning creates complete floor plans automatically. Drones measure lot areas and roofing from aerial photography.
ANSI Z765-2021 specifies that only finished, above-grade space with ceiling height ≥ 7 ft (≥ 5 ft under sloped ceilings) counts as 'living area.' Garages, unfinished attics, and basements are excluded — even finished basements. This standard is referenced in most MLS listing rules.
You need professional tools to measure square footage accurately.
A tape measure (or laser measure) and basic math are sufficient for most residential measurements. Measure the exterior walls for overall house size, then measure each room from wall to wall. The key is systematic room-by-room measurement, recording each dimension immediately.