Square Footage Calculator
Nearly every home project starts with the same question: how many square feet? This calculator finds the area of rectangles, circles, triangles, and L-shaped spaces from a few simple measurements. Results are shown in square feet plus square meters, square yards, and acres, so the same number works for flooring quotes, paint coverage, and lot sizes.
L-shape: length of the first rectangle
L-shape: width of the first rectangle
Area
120ft²
- Square meters
- 11.15m²
- Square yards
- 13.33yd²
- Acres
- 0.0028acre
How it was calculated
- Area = 12 ft × 10 ft = 120.00 ft²
How it works
Rectangle: area = length × width. The workhorse formula — rooms, slabs, and decks are all rectangles until proven otherwise.
Circle: area = π × (diameter ÷ 2)². Measure straight across the circle for the diameter; the radius is half of that.
Triangle: area = ½ × base × height. Height is the perpendicular distance from the base to the opposite corner — not the sloped edge.
L-shape: split the shape into two rectangles and add them: area = (L₁ × W₁) + (L₂ × W₂). Two non-overlapping rectangles always cover an L exactly.
Conversions: square meters = ft² ÷ 10.7639; square yards = ft² ÷ 9; acres = ft² ÷ 43,560.
Worked examples
20 × 15 ft living room
A rectangular living room 20 ft long and 15 ft wide: 20 × 15 = 300 ft². That is 300 ÷ 10.7639 = 27.87 m², 300 ÷ 9 = 33.33 yd², and 300 ÷ 43,560 = 0.0069 acres.
L-shaped patio: 12 × 10 ft plus 6 × 4 ft
Split the L into two rectangles. Rectangle 1: 12 × 10 = 120 ft². Rectangle 2: 6 × 4 = 24 ft². Total: 120 + 24 = 144 ft² (13.38 m², 16 yd²).
How to measure
- Use a tape measure wall-to-wall for rooms; laser measures are faster and just as accurate for long spans.
- For circles, measure the diameter straight across the center — measuring around the edge gives circumference, not diameter.
- For triangles, the height must be perpendicular to the base; eyeballing the sloped side overstates the area.
- Sketch L-shapes on paper first and label each rectangle so the two pieces do not overlap or leave gaps.
- Round each measurement to the nearest half inch; tiny rounding errors do not change material orders.
Assumptions & limitations
Planning estimate
- Calculations assume flat, two-dimensional surfaces — slopes and curved walls need more advanced geometry.
- The L-shape method assumes the two rectangles do not overlap; overlapping pieces double-count area.
- Results are geometric area only — material calculators add their own waste allowances on top.
- No rule-of-thumb constants are used here — every result is exact geometry from your measurements.
Frequently asked questions
Measure the room’s length and width in feet, then multiply: a 12 ft × 10 ft room is 120 ft². Measure wall to wall at the longest and widest points. For an L-shaped room, split it into two rectangles, calculate each, and add them — or use the L-shape option here.
Break it into simple shapes — rectangles, triangles, half-circles — and add the areas. Rectangles cover most of it; triangles handle angled walls via ½ × base × height. Sketch the breakdown on paper first so pieces neither overlap nor leave gaps.
A square yard is 3 ft × 3 ft, so 1 yd² = 9 ft². Carpet and some flooring are priced by the square yard — divide square feet by 9 to convert. A 120 ft² room is 13.33 yd².
One acre is exactly 43,560 ft² — roughly a 208.7 ft square. This calculator shows acres automatically, which is handy when a "room" turns out to be a lot or a field.
For the area itself, no — the geometric result is exact from your measurements. Rounding up happens later: material calculators (flooring, paint, tile) add waste allowances and round to whole boxes, gallons, or bags. Keep this number precise and let each material page do its own rounding.