Square Footage Calculator

To calculate square footage, measure the length and width of the area in feet and multiply them together. For example, a room that is 12 feet long and 10 feet wide is 120 square feet (12 × 10 = 120). That is the entire formula for any rectangular surface.

If your measurements include inches, convert them to feet first by dividing by 12. A length of 10 feet 6 inches becomes 10.5 feet (6 ÷ 12 = 0.5). Working in decimal feet keeps the math simple and avoids mixing units inside the multiplication.

For spaces with multiple sections — like a home with several rooms or a floor with an L-shaped layout — calculate each section separately and add the results. Add 5–10% waste for materials. Full walkthrough: how to calculate square footage.

For a standard rectangular room, measure the longest wall (length) and the perpendicular wall (width), then multiply. A 12 × 10 bedroom is 120 square feet. Measure wall-to-wall at the widest points — baseboards and trim are included in the measurement.

For an L-shaped room, divide the space into two rectangles. Measure each rectangle's length and width, calculate both areas, and add them. For example, an L-shaped room with a 10 × 8 main section and a 6 × 4 alcove is 80 + 24 = 104 square feet.

When measuring for flooring, remember to include closets and doorways — those areas need material too. For paint or wallpaper, subtract openings (doors and windows) from the wall area instead of the floor area. Details: room square footage calculator guide.

To calculate a home's total square footage, measure each finished room individually (length × width in feet) and add the results. Per the ANSI Z765 standard used by US real estate professionals, count only finished, heated, and enclosed living space. Garages, unfinished basements, and open porches are excluded.

For single-family detached homes, measure from the exterior walls — the wall thickness is included in the square footage. For attached homes, townhouses, and condos, measure from the interior unit boundaries (the centerline of shared walls).

For a two-story house, measure each floor separately and add the totals. Stair openings are counted on only one floor (typically the lower level). The total is the ground-floor area plus the second-floor area, not the ground floor doubled. A 1,000 sq ft ground floor with an 800 sq ft second floor is a 1,800 sq ft home.

For any triangle, use the formula Area = ½ × base × height, where the base and height are perpendicular to each other. A triangle with a 10-foot base and 8-foot height has 40 square feet of area (½ × 10 × 8 = 40).

For a right triangle — common in corners and gable ends — the two legs that form the right angle are the base and height. If you only know the three side lengths, use Heron's formula instead: calculate the semi-perimeter s = (a+b+c) ÷ 2, then Area = √(s × (s−a) × (s−b) × (s−c)).

Roof square footage is larger than the building's footprint because pitched roofs have more surface area than flat ground. To estimate: measure the length and width of each roof plane, multiply to get the footprint area, then apply a pitch multiplier based on your roof slope.

Roofing materials are sold in squares — one square covers 100 square feet of roof surface. After calculating total roof square footage, divide by 100 to get the number of squares, then add 10–15% for waste and overlaps.

One acre equals 43,560 square feet. To convert acres to square feet, multiply by 43,560. To convert square feet to acres, divide by 43,560. A quarter-acre lot is 10,890 square feet. Use the acres to square feet converter or the acres square footage guide.

For irregular areas, break the shape into simpler parts — rectangles and triangles — calculate each part, and add the results. An L-shaped yard can be split into two rectangles; a bay window can be split into a rectangle and a triangle.

For a circular area (like a round patio or garden bed), use the formula Area = π × radius². A 10-foot-diameter circle has a 5-foot radius, so the area is π × 5² = about 78.5 square feet.