On this page
Formula
Rectangle = L × W; Triangle = ½ × b × h; Circle = π × (d ÷ 2)²; Total = A₁ + A₂ + …
- L, W
- length and width of a rectangle
- b, h
- base of a triangle and its height measured at a right angle to the base
- d
- diameter of a circle
- A₁, A₂
- areas of the separate rectangles that make up an irregular space
What square footage means
Square footage is the area of a flat surface measured in square feet, where one square foot is a square 1 ft on each side. It’s the number you need to buy flooring, tile, sod, roofing or paint, to compare home listings, and to price work that contractors charge per square foot. This square footage calculator also gives the area in square yards (used for carpet) and square meters (used on most imported products).
How to use the square footage calculator
- Choose the shape: Rectangle, Triangle, Circle or Multiple areas.
- Enter the measurements. In the single-shape tabs each field has its own unit, so 132 inches × 10 feet works without converting.
- For irregular rooms, use Multiple areas and enter up to four rectangles in one unit.
- Keep the 10% waste allowance for ordering material, or set it to 0 if you only need the area.
- Optionally enter a price per square foot, square yard or square meter to estimate the cost.
The headline figure is always the measured area. The waste allowance only affects the “area with waste” line and the cost, so you can see both numbers side by side.
How to calculate square footage by hand
Rectangles and squares
Multiply length by width. A dining room 11.5 ft × 13 ft is 11.5 × 13 = 149.5 ft². If you measured in inches, divide the result by 144 (12 × 12): 138 in × 156 in = 21,528 in², and 21,528 ÷ 144 = 149.5 ft².
Triangles
Multiply the base by the height and halve it. The height must be measured at a right angle to the base, not along the sloping side. A triangular corner bed with a 7 ft base and a 4 ft height is ½ × 7 × 4 = 14 ft². If you only know the three sides of a right triangle, the Pythagorean theorem calculator finds the missing one.
Circles
Halve the diameter, square it and multiply by π. A round patio 10 ft across has a radius of 5 ft: 3.14159 × 25 = 78.54 ft². For a half circle, divide by 2.
L-shaped and irregular rooms
Draw the room and split it into rectangles that don’t overlap. An L-shaped kitchen might be a 14 × 10 ft main area plus an 8 × 6 ft breakfast nook: 140 + 48 = 188 ft². Bay windows and alcoves can be added as small rectangles or triangles.
Common room sizes in square feet
These areas were calculated with the square footage calculator. The last column adds the default 10% allowance you’d use when ordering flooring.
| Room size | Square feet | Square yards | Square meters | With 10% waste |
|---|---|---|---|---|
| 10 × 10 ft | 100 | 11.11 | 9.29 | 110 ft² |
| 12 × 12 ft | 144 | 16 | 13.38 | 158.4 ft² |
| 12 × 14 ft | 168 | 18.67 | 15.61 | 184.8 ft² |
| 14 × 16 ft | 224 | 24.89 | 20.81 | 246.4 ft² |
| 15 × 20 ft | 300 | 33.33 | 27.87 | 330 ft² |
| 20 × 20 ft | 400 | 44.44 | 37.16 | 440 ft² |
| 25 × 40 ft | 1,000 | 111.11 | 92.9 | 1,100 ft² |
Converting between square units
Area units scale by the square of the length conversion. Because 1 yard is 3 feet, 1 square yard is 3 × 3 = 9 square feet, not 3. Because 1 foot is 0.3048 m, 1 square foot is 0.3048² = 0.09290304 m². Here are the factors you’ll use most:
- Square feet ÷ 9 = square yards
- Square feet × 0.0929 = square meters
- Square meters × 10.764 = square feet
- Square feet ÷ 43,560 = acres
For lengths, the length converter handles feet, inches, yards and meters.
Where you’ll use it
- Flooring and tile: take the total from this page into the flooring calculator or the tile calculator to turn it into boxes or tiles.
- Painting: wall area is length × height, minus doors and windows. The paint calculator does that subtraction and converts the area to gallons.
- Concrete and gravel: multiply the area by the depth in feet to get cubic feet, or use the concrete calculator.
- Pricing work: contractors often quote per square foot. Enter the rate in the square footage calculator’s price field to estimate the total.
Common mistakes
- Mixing feet and inches. 12 ft 6 in is 12.5 ft, not 12.6 ft. Divide the inches by 12.
- Dividing square feet by 3 for square yards. The correct divisor is 9.
- Using the slanted side of a triangle as its height. The height is the perpendicular distance from the base to the opposite corner.
- Counting overlaps twice. When you split an L-shape, make sure the rectangles don’t share any floor.
- Measuring baseboard to baseboard for flooring. Flooring runs under the trim, so measure wall to wall.
Glossary
- Square foot (ft², sq ft): the area of a 1 ft × 1 ft square, 144 in².
- Square yard (yd²): 9 ft², the usual unit for carpet.
- Square meter (m²): about 10.76 ft².
- Waste allowance: extra material bought to cover cuts, offcuts and mistakes.
Worked examples
A rectangular bedroom with a flooring budget
A 13.5 ft × 11 ft bedroom, 10% waste, flooring at $4.25 per square foot.
Inputs (Rectangle): Length = 13.5; Length unit = Feet; Width = 11; Width unit = Feet; Waste allowance = 10 %; Material price (optional) = $4.25; Price unit = per square foot
Area = 13.5 ft × 11 ft = 148.5 ft² With waste: 148.5 ft² × 1.1 = 163.35 ft² Cost: 163.35 × $4.25 = $694.24
Answer: Area of the rectangle: 148.5 ft² (13.8 m²). With 10% waste, plan for 163.35 ft².
An L-shaped living area split into two rectangles
An 18 × 12 ft main area plus a 9 × 7.5 ft nook, measured in feet, 10% waste.
Inputs (Multiple areas): Measurements in = Feet; Area 1 length = 18; Area 1 width = 12; Area 2 length = 9; Area 2 width = 7.5; Waste allowance = 10 %
Area 1: 18 ft × 12 ft = 216 ft² Area 2: 9 ft × 7.5 ft = 67.5 ft² Total: 216 + 67.5 = 283.5 ft² With waste: 283.5 ft² × 1.1 = 311.85 ft²
Answer: Area of 2 areas combined: 283.5 ft² (26.34 m²). With 10% waste, plan for 311.85 ft².
A round patio measured in meters
A circular patio 3.6 m across, 5% waste for edge cuts.
Inputs (Circle): Diameter = 3.6; Diameter unit = Meters; Waste allowance = 5 %
Area = π × (3.6 m ÷ 2)² = 10.18 m² With waste: 10.18 m² × 1.05 = 10.69 m²
Answer: Area of the circle: 10.18 m² (109.56 ft²). With 5% waste, plan for 10.69 m².
A triangular garden bed (edge case: no waste)
A triangle with a 96-inch base and a 5 ft perpendicular height, with no waste added. Mixed units are converted to feet first.
Inputs (Triangle): Base = 96; Base unit = Inches; Height (perpendicular to the base) = 5; Height (perpendicular to the base) unit = Feet; Waste allowance = 0 %
Area = ½ × 8 ft × 5 ft = 20 ft²
Answer: Area of the triangle: 20 ft² (1.86 m²). With 0% waste, plan for 20 ft².
Assumptions and limitations
- This is an estimate only, not engineering or surveying advice. Real rooms are rarely perfectly square, so measure each wall and use the larger figure.
- Mixed units are allowed in the single-shape modes (for example inches × feet). Every measurement is converted to feet, or to meters when the first measurement is metric, before multiplying.
- Conversions use the exact definitions 1 ft = 0.3048 m and 1 yd² = 9 ft², the factors listed by NIST.
- The waste allowance defaults to 10% if left empty. It is added only to the "area with waste" and cost figures; the headline result is the bare measured area. 10% suits flooring in a straight layout; use 15% for diagonal layouts or awkward shapes.
- The optional price is applied to the area with waste, in the price unit you choose (per square foot, square yard or square meter).
- Results are rounded to 2 decimal places.
Frequently asked questions
How do I calculate square footage of a room?
Measure the length and width in feet and multiply them. A room 11 ft by 15 ft is 11 × 15 = 165 square feet. If a measurement includes inches, convert them to a decimal of a foot first, so 11 ft 6 in becomes 11.5 ft.
How do you calculate square footage of an L-shaped room?
Split it into two rectangles that don't overlap, find the area of each and add them. Use the Multiple areas tab to enter each rectangle; it shows the area of every part and the total.
How many square feet are in a square yard?
Nine. A square yard is 3 ft × 3 ft, so divide square feet by 9 to get square yards. Carpet is often priced per square yard, and 180 ft² is 20 yd².
How do I convert square feet to square meters?
Multiply by 0.09290304, or divide by about 10.764. A 200 ft² room is 18.58 m².
How do you find the square footage of a circle?
Halve the diameter to get the radius, square it and multiply by π (3.14159). A round rug area 6 ft across has a radius of 3 ft, so its area is 3.14159 × 9 = 28.27 ft².
Does square footage include closets and hallways?
For buying flooring, include every space that gets the same material, closets and hallways included. For a home's listed living area, rules differ by market and appraisal standard, so check the standard your lender or listing service uses.
Sources
- NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity — National Institute of Standards and Technology. Checked October 12, 2026.
- How To Measure for Flooring — Ferguson Home. Checked October 12, 2026.