Glossary of measurement and square footage terms

A — D

• ·Above-Grade — Any portion of a building that is at or above ground level. Real estate appraisals typically count only above-grade square footage as part of the official Gross Living Area (GLA). Finished basements are reported separately even if heated and habitable.
• ·Acre — A unit of land area equal to 43,560 square feet, 4,840 square yards, or about 4,047 square meters. Used primarily for lots, farms, and commercial parcels. A standard American football field (without end zones) is roughly 1.1 acres.
• ·ANSI Z765 — The American National Standards Institute standard for measuring single-family residential properties. Defines how appraisers and real estate agents calculate finished square footage in detached homes. Measure to exterior walls, count only finished and heated above-grade areas, and exclude open-to-below spaces.
• ·Annulus — A ring-shaped region between two concentric circles. Used to calculate the area of doughnut-shaped spaces like circular walkways around a pool. Formula: π × (R² − r²), where R is the outer radius and r is the inner radius.
• ·Area — A two-dimensional measurement of the surface a shape covers, expressed in square units (sq ft, sq m, etc.). Square footage is one specific way of expressing area. Distinct from perimeter (which is one-dimensional) and volume (three-dimensional).
• ·Base — In a triangle, the side chosen as the reference for measuring height. Any side of a triangle can serve as the base, but height must always be measured perpendicular to whichever base you choose. Triangle area = (Base × Height) ÷ 2.
• ·Blueprint — A detailed scaled drawing showing the layout, dimensions, and construction details of a building or space. Modern blueprints typically include a square footage summary on the title sheet listing finished, unfinished, and total areas separately.
• ·BOMA — Building Owners and Managers Association. Publishes the BOMA standard for measuring office and commercial space, which differs from residential ANSI Z765. BOMA defines Usable Area, Rentable Area, and Common Area Load Factor for commercial leases.
• ·Coverage Rate — How much surface area a given quantity of material covers. Examples: 1 gallon of paint covers 350-400 sq ft on one coat; one bundle of asphalt shingles covers ~33 sq ft. Coverage rates are listed by manufacturers and used to convert square footage into material quantities.
• ·Diameter — A straight line passing through the center of a circle, touching both edges. Equal to twice the radius. Often easier to measure on real-world circles (like pools or tanks) than the radius, since you can pull a tape across the widest point.
• ·Dimension — A single measured extent (length, width, height, radius). Square footage calculations require two dimensions for most shapes, three for an annulus or trapezoid.
• ·Drop — In carpet installation, the length of a single piece of carpet rolled out from a 12-ft-wide bolt. Calculating drops accurately is more important than raw square footage when ordering carpet, because seams and pile direction matter.

E — L

• ·Exterior Square Footage — The total square footage of a building measured to the outside of exterior walls. Larger than interior square footage by the wall thickness on all sides (typically 4-8% more). Used in ANSI Z765 residential appraisals and most real estate listings.
• ·Footprint — The ground-level outline of a building or structure, measured to its outermost walls. Footprint is the area a building covers on the lot but does not include upper floors. A 2-story house with a 1,200 sq ft footprint typically has 2,400 sq ft of total above-grade living area.
• ·Formula — A mathematical rule for calculating area from one or more dimensions. Different shapes use different formulas: rectangle (L × W), circle (πr²), triangle ((B × H) ÷ 2), trapezoid (((B₁ + B₂) ÷ 2) × H).
• ·GBA — Gross Building Area. The total floor area of a building including all enclosed spaces, measured to the outside of the exterior walls. Includes finished and unfinished space, basements, and mechanical rooms. Used in commercial appraisals and tax assessments.
• ·GLA — Gross Living Area. The finished, heated, above-grade square footage of a residential property used in real estate appraisal. Excludes garages, unfinished basements, and open-to-below areas. The number that appears on most listings.
• ·Heated Square Footage — Floor area served by a permanent heating system (forced air, radiant, baseboard). Most real estate definitions of livable square footage require the space to be heated. Sunrooms or screened porches are typically excluded.
• ·Heron's Formula — A method for calculating the area of a triangle when you know all three side lengths but not the height. Formula: Area = √(s × (s−a) × (s−b) × (s−c)), where s = (a + b + c) ÷ 2 is the semi-perimeter.
• ·Hectare — A metric unit of land area equal to 10,000 square meters or about 2.47 acres or 107,639 sq ft. Used internationally for agricultural and large-parcel measurements.
• ·Height — The vertical or perpendicular dimension of a shape. In a triangle, height is measured perpendicular from the base to the opposite vertex - not along a side. In wall-area calculations, height is the floor-to-ceiling distance.
• ·Interior Square Footage — The floor area measured between interior wall surfaces. Smaller than exterior square footage by the thickness of the exterior walls. Used for flooring, paint, and material estimates - not typically for real estate listings.
• ·Length — The longer of the two main dimensions of a rectangle (width is the shorter). When the rectangle is a wall, length usually refers to its horizontal extent. Always measure length and width perpendicular to each other.
• ·Linear Foot — A one-dimensional unit of length equal to 12 inches. Used for trim, baseboards, fencing, countertop edges, and railings - anything sold by length rather than area. Distinct from square feet (area) and cubic feet (volume).
• ·Livable Square Footage — Real estate term for the finished, heated, above-grade space inside a home. Synonymous with Gross Living Area in most markets. Excludes garages, open porches, attics with limited ceiling height, and unfinished spaces.

M — R

• ·Material Estimator — A calculation that converts square footage plus a coverage rate or unit size into the quantity of material needed (gallons, boxes, bundles, rolls). Most calculators on this site include a material estimator.
• ·MGA — Mean Ground Area, the average ground-level footprint of a multi-story building. Less common than GLA or GBA. Mostly used in zoning and planning documents.
• ·Net Area — The square footage of a surface after subtracting non-paintable, non-floorable, or non-livable openings (doors, windows, fireplaces, stairs). Always smaller than gross area. Net area is what you actually need to cover with material.
• ·Obstruction — Any feature that interrupts a flat surface and reduces usable square footage. Common obstructions: doors, windows, fireplaces, columns, kitchen islands, built-in cabinetry. Subtract obstructions for paint and wallpaper but include them in floor area for material orders (you'll cut around them but still pay for the cuts).
• ·Open-to-Below — A floor area on an upper level that overlooks a lower level (typically a foyer or great room). Open-to-below areas are NOT counted in upper-floor square footage under ANSI Z765 - they are part of the lower floor only.
• ·Parallelogram — A four-sided shape with both pairs of opposite sides parallel. Includes rectangles, squares, and rhombuses as special cases. Area formula: Base × Height (where height is the perpendicular distance between the two base sides).
• ·Perimeter — The total length around the boundary of a shape, expressed in linear feet (not square feet). Used to calculate baseboard, fencing, or trim. A 10 ft × 12 ft rectangle has a perimeter of 44 linear feet but an area of 120 sq ft.
• ·π (Pi) — The mathematical constant equal to approximately 3.14159265. Appears in every circle and circular-segment formula. Most calculators use 3.14159 or 3.1416, which is accurate enough for any construction or DIY purpose.
• ·Plan View — A drawing that shows a space as if viewed from directly above, with all walls and features projected to a flat plane. The standard view used for square footage calculation. Distinct from elevation (side view) or section (cutaway view).
• ·Pythagorean Theorem — a² + b² = c². Used to find the diagonal of a rectangle or to calculate triangle dimensions when only two sides are known. Useful when one wall in a room is missing and you need to back-calculate from the diagonal.
• ·Quadrilateral — Any four-sided shape. Includes squares, rectangles, parallelograms, rhombuses, trapezoids, and irregular four-sided shapes. Each subtype has its own area formula.
• ·Radius — The distance from the center of a circle to any point on its edge. Equal to half the diameter. The radius is the input most circle area formulas (πr²) require. To measure radius on a real-world circle, find the center first, then measure outward.
• ·Rectangle — A four-sided shape with four right angles and opposite sides of equal length. Most rooms approximate rectangles. Area = Length × Width.
• ·Rentable Area — In commercial real estate (BOMA standard), the total area for which a tenant pays rent. Includes the tenant's usable square footage plus a pro-rata share of common areas (lobbies, hallways, restrooms). Always larger than the actual occupied space.

S — Z

• ·Sector — A pie-slice-shaped region of a circle bounded by two radii and an arc. Area = (θ ÷ 360) × π × r², where θ is the central angle in degrees. Used for curved patios, garden beds, and circular building extensions.
• ·Segment — A portion of an irregular shape that has been broken down into a simpler geometric form for calculation. The standard approach for irregular rooms is to divide them into rectangles, triangles, and circular segments, calculate each, and sum the results.
• ·Slope — The angle or pitch of a roof or floor. Affects the actual surface area of a roof: a 1,500 sq ft footprint with a steep 12/12 pitch has a roof surface area of about 2,121 sq ft. Always factor in slope for roofing material estimates.
• ·Square — A four-sided shape with four equal sides and four right angles. A special type of rectangle. Area = Side × Side (or Side²).
• ·Square (Roofing) — A unit of roofing area equal to 100 square feet. Roofing materials (shingles, underlayment, ice-and-water shield) are often sold by the square. A 2,200 sq ft roof requires 22 squares of material.
• ·Square Foot (sq ft, ft²) — The most common unit of area in U.S. construction and real estate. Equals the area of a square that measures one foot on each side. 144 square inches in 1 sq ft. 9 sq ft in 1 sq yd. 43,560 sq ft in 1 acre.
• ·Square Inch (sq in, in²) — A small unit of area equal to a 1-inch square. 144 sq in in 1 sq ft. Used for very small surfaces like tile patterns or cabinet hardware.
• ·Square Meter (sq m, m²) — The metric standard for area. 1 sq m = 10.7639 sq ft. Used in international real estate listings and metric construction. Convert sq ft to sq m by dividing by 10.7639.
• ·Square Yard (sq yd, yd²) — A unit of area equal to 9 square feet (a 3 ft × 3 ft square). Carpet was traditionally sold by the square yard but is now more commonly priced by the square foot in the U.S. Still standard for some landscaping and concrete materials.
• ·Trapezoid — A four-sided shape with one pair of parallel sides (called bases) and two non-parallel sides. Area = ((Base₁ + Base₂) ÷ 2) × Height. Used for tapered rooms, sloped lots, and architectural alcoves.
• ·Triangle — A three-sided shape. Area = (Base × Height) ÷ 2 if you know base and perpendicular height, or use Heron's Formula if you know all three sides. The most common shape for gable walls, attics, and triangular garden beds.
• ·Unit Conversion — The process of changing a measurement from one unit to another (e.g., square feet to square meters). Always convert at the end of the calculation, not during, to minimize rounding errors.
• ·Usable Area — In commercial real estate (BOMA), the actual floor area a tenant can occupy with furniture and people. Excludes structural columns, vertical penetrations (elevators, stairwells), and corridors that serve other tenants. Smaller than rentable area.
• ·Vertex — A corner point of a polygon. Triangles have 3 vertices, rectangles have 4, an L-shape has 6. Counting vertices is a quick way to sanity-check that you've measured every wall in an irregular room.
• ·Volume — A three-dimensional measurement (length × width × height), expressed in cubic units (cu ft, cu m). Distinct from area. Used for HVAC sizing, mulch ordering, and concrete pours - not for typical square footage calculations.
• ·Waste Factor — An additional percentage of material added to the calculated square footage to account for cuts, breakage, mistakes, and future repairs. Typical values: 5% for paint, 10% for tile and laminate, 15% for diagonal tile or carpet, 20%+ for natural stone or pattern-matched flooring.
• ·Width — The shorter of the two main dimensions of a rectangle (length is the longer). When the rectangle is a wall, width usually refers to vertical extent. Always measured perpendicular to length.
• ·Yard (yd) — A linear unit equal to 3 feet or 36 inches. Distinct from a square yard (area) or cubic yard (volume).

Industry standards referenced on this site

When this site references a measurement standard, here is what we mean. These are the published references that contractors, appraisers, and architects use day-to-day.