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The House Square Footage Calculator adds up a home room by room. For a rectangle it multiplies length by width; an L-shaped room is split into two rectangles and added; a triangle is half the base times the height, a circle π times the radius squared and a trapezoid the average of the two parallel sides times the height. Inches, yards and meters are converted to feet first with the exact international foot of 0.3048 m that NIST specifies, and the area is shown in square feet, square yards (÷ 9), square meters (× 0.09290304) and acres (÷ 43,560), times the number of identical areas and priced at your cost per square foot. Following the ANSI Z765 method from Home Innovation Research Labs, the total is reported to the nearest whole square foot; for a house, Z765 counts only finished area with a ceiling at least 7 ft high and reports below-grade area separately. A 12 × 15 ft room is 180 sq ft, 20 sq yd or 16.72 m²; an L-shaped room of 20 × 12 ft plus 10 × 8 ft is 320 sq ft.
Square footage is length × width in feet. Split an L-shaped room into two rectangles and add them; a triangle is ½ × base × height and a circle π × radius². NIST defines the foot as exactly 0.3048 m, so 1 sq ft = 0.09290304 m²; there are 9 sq ft in a square yard and 43,560 in an acre. ANSI Z765 reports a house to the nearest whole square foot and counts only finished area with a ceiling of at least 7 ft (6 ft 4 in under beams and ducts).
| Room | Square feet | Square yards | Square meters |
|---|---|---|---|
| 10 × 10 ft | 100 | 11.1 | 9.29 |
| 10 × 12 ft | 120 | 13.3 | 11.15 |
| 12 × 12 ft | 144 | 16.0 | 13.38 |
| 12 × 15 ft | 180 | 20.0 | 16.72 |
| 14 × 16 ft | 224 | 24.9 | 20.81 |
| 16 × 20 ft | 320 | 35.6 | 29.73 |
| 20 × 24 ft | 480 | 53.3 | 44.59 |
| 24 × 24 ft | 576 | 64.0 | 53.51 |
Multiply the length by the width, both in feet. A room 12 ft by 15 ft is 12 × 15 = 180 sq ft. For an L-shaped room, split it into two rectangles, work each one out and add them: 20 × 12 plus 10 × 8 is 240 + 80 = 320 sq ft.
NIST defines the foot as exactly 0.3048 m, so 1 sq ft = 0.09290304 m². 180 sq ft is 16.72 m². There are 9 sq ft in a square yard, so 180 sq ft is 20 sq yd, and 43,560 sq ft in an acre.
A circle is π × radius²: a 10 ft diameter circle is 3.1416 × 5 × 5 = 78.54 sq ft. A triangle is half the base times the height: a 12 ft base and 8 ft height is 48 sq ft.
Under the ANSI Z765 method from Home Innovation Research Labs, finished square footage counts finished areas with a ceiling at least 7 ft high (6 ft 4 in under beams and ducts). Under a sloped ceiling at least half the room must be 7 ft and nothing under 5 ft counts. Openings to the floor below are excluded, and finished basement area is reported separately as below-grade.
ANSI Z765 measures a house to the nearest inch or tenth of a foot and reports the final figure to the nearest whole square foot. For buying materials, measure each room at its widest points and add the waste allowance the material's maker recommends.
Turning the area into material? The flooring calculator adds the maker's waste allowance and counts cartons.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.