Square Feet, Meters & Acres
Last reviewed: May 2026
Calculate the area of any geometric shape — from simple rectangles and circles to complex polygons. Area calculations are essential for flooring, painting, landscaping, roofing, and land measurement. This calculator handles all common shapes and converts between square feet, square meters, square yards, and acres.1
| Shape | Formula | Example |
|---|---|---|
| Rectangle | L × W | 12 × 15 = 180 sq ft |
| Circle | πr² | π × 5² = 78.54 sq ft |
| Triangle | b × h / 2 | 8 × 6 / 2 = 24 sq ft |
| Trapezoid | (a + b) × h / 2 | (6 + 10) × 4 / 2 = 32 sq ft |
| Ellipse | π × a × b | π × 5 × 3 = 47.12 sq ft |
| Unit | Equals |
|---|---|
| 1 sq ft | 0.0929 sq m / 144 sq in |
| 1 sq m | 10.764 sq ft |
| 1 sq yd | 9 sq ft |
| 1 acre | 43,560 sq ft / 4,047 sq m |
| 1 hectare | 2.471 acres / 10,000 sq m |
| Shape | Formula | Variables | Example |
|---|---|---|---|
| Rectangle | A = l × w | l = length, w = width | 12 × 8 = 96 sq units |
| Triangle | A = ½ × b × h | b = base, h = height | ½ × 10 × 6 = 30 sq units |
| Circle | A = π × r² | r = radius | π × 5² = 78.54 sq units |
| Trapezoid | A = ½ × (a + b) × h | a, b = parallel sides, h = height | ½ × (8 + 12) × 5 = 50 sq units |
| Parallelogram | A = b × h | b = base, h = perpendicular height | 9 × 7 = 63 sq units |
| Ellipse | A = π × a × b | a, b = semi-axes | π × 6 × 4 = 75.40 sq units |
| Regular polygon | A = ½ × p × a | p = perimeter, a = apothem | ½ × 30 × 4.33 = 64.95 sq units |
The height in these formulas always refers to the perpendicular distance — the straight vertical drop from the top to the base, not the slanted side length. This is the most common mistake in area calculations: using the slant height of a triangle or parallelogram instead of the perpendicular height produces an incorrect (always too large) result. If you know side lengths but not the height, trigonometry or Heron's formula (for triangles) can derive the area without a separate height measurement.
Most real-world area problems involve rooms, yards, and irregular spaces that are not perfect geometric shapes. The approach for irregular areas is decomposition: break the space into rectangles, triangles, and other standard shapes, calculate each area separately, then sum the results. An L-shaped room can be split into two rectangles. A room with a bay window adds a trapezoid or triangle to the main rectangle. For curved boundaries like garden beds, approximate with a series of small rectangles or use the planimeter method — measure the widths at regular intervals along the length and average them, then multiply by the total length. Our Square Footage Calculator specializes in room-specific area calculations with these techniques built in.
| From | To | Multiply By | Common Use |
|---|---|---|---|
| Square feet | Square meters | 0.0929 | International property comparison |
| Square meters | Square feet | 10.764 | US property listings |
| Square feet | Acres | 0.0000229568 | Land area |
| Acres | Square feet | 43,560 | Lot sizing |
| Square meters | Hectares | 0.0001 | Agricultural land |
| Square miles | Acres | 640 | County/regional area |
The key detail with area conversions: the conversion factor is the square of the linear factor. One foot equals 0.3048 meters, but one square foot equals 0.3048² = 0.0929 square meters. This squared relationship means small linear measurement errors compound when calculating area — a 2% error in measuring a room's length and width produces a 4% error in the computed area. Always measure at least twice for important area calculations like flooring orders or property assessments.
Accurate area measurement drives material purchasing for virtually every home improvement project. Flooring materials are sold by the square foot — measure the room area and add 10% for waste (cuts and fitting). Paint coverage is calculated by wall area: wall area = perimeter × ceiling height, minus window and door openings. One gallon of paint covers approximately 350–400 square feet with one coat. Sod and seed for lawns require the yard area in square feet, with sod adding 5% for cutting waste. Roofing is measured in "squares" (1 square = 100 square feet), with pitch-adjusted area calculated by multiplying the footprint area by the roof pitch factor. Getting the area right prevents both the frustration of running short mid-project and the cost of over-ordering materials you cannot return.
| Project | Cost per Sq Ft | 200 sq ft Room | 500 sq ft Room |
|---|---|---|---|
| Hardwood flooring (installed) | $8–$15 | $1,600–$3,000 | $4,000–$7,500 |
| Carpet (installed) | $3–$8 | $600–$1,600 | $1,500–$4,000 |
| Tile (installed) | $10–$20 | $2,000–$4,000 | $5,000–$10,000 |
| Interior painting | $2–$5 | $400–$1,000 | $1,000–$2,500 |
| Drywall (installed) | $2–$4 | $400–$800 | $1,000–$2,000 |
Per-square-foot pricing allows quick budget estimates for any room size. Multiply the room area by the per-square-foot rate, then add 10–15% for materials waste and unexpected complications. These estimates help you evaluate contractor bids, compare material options, and set realistic project budgets before committing to any purchase. See our Flooring Calculator for material-specific area calculations with waste factored in.
When shapes resist simple decomposition, several techniques estimate area effectively. The grid method overlays a grid of squares on the shape and counts complete squares plus estimates of partial squares — suitable for organic shapes like garden beds or ponds. The coordinate method uses the Shoelace formula: list the (x, y) coordinates of each vertex in order, then apply A = ½|Σ(xᵢyᵢ₊₁ − xᵢ₊₁yᵢ)| — this works for any polygon regardless of shape. For curved boundaries, Simpson's rule approximates the area by measuring the width at equally spaced intervals: A ≈ (d/3)(y₀ + 4y₁ + 2y₂ + 4y₃ + ... + yₙ), where d is the interval spacing. GPS-based area apps use the coordinate method in real time, allowing you to walk the perimeter of a property and calculate its area automatically — accuracy of 1–2% is typical for areas above 1,000 square feet.
Area calculations serve different purposes depending on context. Floor area (footprint) measures horizontal space and determines room capacity, furniture layout, and property value — the metric used in real estate listings. Surface area measures the total exposed surface of a 3D object and applies to painting, coating, heat transfer, and material coverage. A 10×12 room has 120 square feet of floor area but 472 square feet of wall and ceiling surface area (assuming 8-foot ceilings and no windows). Understanding which type of area you need prevents costly errors: ordering 120 square feet of paint for a room that actually has 472 square feet of paintable surface means running out before finishing even the first coat. Use our Paint Calculator for surface-area-based paint estimates.
Property area measurements directly impact value — price per square foot is the standard metric for comparing properties across different sizes. In most US markets, livable square footage includes all heated and cooled rooms with finished walls, floors, and ceilings. Garages, unfinished basements, covered porches, and attics typically do not count toward livable area, though they add value separately. A common source of confusion: property tax assessments may use different area calculations than real estate listings, and appraisers may disagree with listing agents about what qualifies as "finished" space. If an appraiser measures your home at 1,800 square feet but the listing says 2,000 because it included the finished basement, the lower figure affects your sale price and property tax assessment. Always verify how area is measured in your jurisdiction.
Residential lots in the US are typically measured in acres or square feet. A standard suburban lot ranges from 7,000 to 15,000 square feet (roughly 0.16 to 0.34 acres). Rural properties are measured in acres, with 1 acre equaling 43,560 square feet — roughly the size of a football field without end zones. For irregularly shaped lots, hire a surveyor or use county GIS maps that provide parcel boundaries with computed areas. When evaluating buildable area, subtract setback requirements (typically 10–25 feet from each boundary where construction is prohibited), easements, and any flood zones or wetland areas. A 0.5-acre lot with 25-foot setbacks on all sides may have an effective buildable area of only 0.25–0.30 acres. See our Fence Calculator to estimate perimeter-based costs for your lot, and our Gravel Calculator for area-based material estimates.
Area and perimeter are related but independent measurements. Shapes with the same perimeter can have vastly different areas — and vice versa. A 10×10 square has perimeter 40 and area 100. A 15×5 rectangle also has perimeter 40 but area only 75. A circle with perimeter (circumference) 40 has area approximately 127. This mathematical fact has practical implications: when maximizing enclosed area with a fixed amount of fencing, a circle is optimal, followed by a square; long narrow rectangles are the least efficient. For gardens, paddocks, or any fenced area, choosing a square or near-square shape gives you 20–30% more usable area than a long narrow shape with the same fencing material. Use our Perimeter Calculator to explore this relationship with your specific dimensions.
Accurate area measurement starts with reliable length measurements. Laser distance measurers ($30–$80) provide accuracy within 1/16 inch over distances up to 100+ feet — far more precise and faster than tape measures for large rooms. For outdoor areas, GPS-based measurement apps achieve 1–2% accuracy for plots above 1,000 square feet. Professional surveys use total stations and differential GPS for sub-inch accuracy on property boundaries and construction sites. For quick estimates, use the stride method: most adults have a stride length of 2.5–3 feet, so pacing off a space gives a rough area estimate within 10–15%. When precision matters — flooring orders, material quantities, property transactions — always use instruments and measure at least twice.
→ Divide irregular rooms. Break into rectangles, calculate each, sum.
→ Measure twice. Area errors double the material error.
→ For paint/flooring: Area ÷ coverage rate = material needed.
→ Remember πr². Circle area uses radius (half the diameter), not the full diameter.
See also: Perimeter · Percentage · Length Converter · Paint