Measurement
Square Footage Calculator
Use this square footage calculator to find the area of a room, floor, patio, lawn or lot in square feet. Add rectangles, circles, triangles and trapezoids together, subtract cut-outs, and get the total in square feet, square yards, square meters and acres, with the working shown.
Result
Enter your measurements and press Calculate. What to buy, the working and the cost will appear here.
How to use the square footage calculator
- Pick a shape for the first area: rectangle, square, circle, triangle or trapezoid.
- Enter its measurements. Type decimals (
12.5) or feet and inches (12' 6"), and choose feet, inches, meters or centimeters beside each box. - Add more areas for L-shaped rooms, closets or several rooms at once. Set How many for identical rooms.
- Subtract cut-outs such as a kitchen island, fireplace hearth or pool by setting an area to Subtract.
- Press Calculate. You get the total square footage, the same area in other units, and each step of the calculation.
Square footage formulas
Square footage is an area, so every formula multiplies two measurements in feet and gives square feet (ft²). Measure in the same unit throughout, or let the calculator convert for you.
| Shape | Formula | Example |
|---|---|---|
| Rectangle | length × width | 12 ft × 10 ft = 120 ft² |
| Square | side × side | 9 ft × 9 ft = 81 ft² |
| Circle | π × radius² (radius = diameter ÷ 2) | 10 ft across: 3.1416 × 5² = 78.54 ft² |
| Triangle | ½ × base × height | ½ × 10 ft × 6 ft = 30 ft² |
| Trapezoid | ½ × (side a + side b) × height | ½ × (8 + 12) × 5 = 50 ft² |
For an irregular space, split it into these shapes, work out each one and add them up. That is exactly what the Add another area button does.
Worked example: an L-shaped room
A living room measures 14 ft × 12 ft and opens into an 8 ft × 6 ft dining nook. A 3 ft × 3 ft tiled hearth in front of the fireplace will not be carpeted. Split the room into two rectangles and subtract the hearth:
- Area 1 – Rectangle: 14 ft × 12 ft = 168 ft²
- Area 2 – Rectangle: 8 ft × 6 ft = 48 ft²
- Area 3 – Square (subtracted): 3 ft × 3 ft = 9 ft²
- Total: 168 ft² + 48 ft² − 9 ft² = 207 ft²
The room is 207 ft², which is 23 yd² or 19.23 m². Open this example in the calculator to change the numbers.
How to measure a room for square footage
- Measure wall to wall at floor level, along the longest straight lines. Round to the nearest inch; small errors on both sides roughly cancel out.
- Sketch the floor plan first. Draw the outline, split it into rectangles, and write each measurement on the sketch before entering it.
- Closets and alcoves are separate small rectangles. Include them if the flooring, paint or carpet will go there too.
- Bay windows and angled corners are usually a trapezoid or triangle added to the main rectangle.
- Curved areas such as a round patio or a planting bed are circles; measure straight across the widest point for the diameter.
- Leave out areas that the material will not cover: fixed cabinets, kitchen islands, tubs or a hearth. Enter them as Subtract.
Square footage conversions
Use these to convert square feet to other units. The calculator does this automatically in the result.
| Unit | Equals | 1 ft² equals |
|---|---|---|
| 1 square inch | 0.00694444 ft² | 144 in² |
| 1 square yard | 9 ft² | 0.1111 yd² |
| 1 square meter | 10.7639 ft² | 0.0929 m² |
| 1 acre | 43,560 ft² | 0.00002296 acres |
| 1 hectare | 107,639 ft² | 0.00000929 ha |
To turn square feet into square yards, divide by 9. To turn square feet into square meters, multiply by 0.0929. One acre is 43,560 square feet.
Using your square footage to buy materials
Square footage is the starting point for most material estimates, but it is not what you buy. Flooring, tile and sod need a waste allowance for cuts; paint depends on wall area rather than floor area; and concrete and gravel need a depth to become a volume. For those jobs, go straight to the matching calculator:
- Flooring calculator for boxes of laminate, vinyl plank or hardwood.
- Paint calculator for gallons based on wall height, doors and windows.
- Concrete calculator or cubic yard calculator when you add a depth.
Assumptions and limitations
- Results are flat (plan) areas. A sloped roof or a staircase has more surface than its footprint; use the roofing calculator for roofs.
- No waste allowance is added here, because the right allowance depends on the material.
- Real rooms are rarely perfectly square. For expensive materials, measure each wall and use the larger figure.
- Listing or appraisal square footage of a home follows specific measuring standards (for example, exterior measurements and rules for stairs and low ceilings). This calculator measures what you enter; it is not an appraisal.
Square footage questions
How do I calculate the square footage of a room?
Measure the length and width in feet and multiply them. A room 12 ft long and 10 ft wide is 12 × 10 = 120 square feet. For L-shaped or irregular rooms, split the floor into rectangles, find each area and add them together.
How many square feet is a 12 × 12 room?
A 12 ft × 12 ft room is 144 square feet (16 square yards, or about 13.4 m²).
How do I work out square footage when measurements are in feet and inches?
Convert the inches to a decimal of a foot by dividing by 12 (6 inches = 0.5 ft), then multiply. 12 ft 6 in × 10 ft 3 in is 12.5 × 10.25 = 128.13 ft². You can also type 12' 6" straight into the calculator.
How do I convert square feet to square yards?
Divide square feet by 9, because a square yard is 3 ft × 3 ft. 360 ft² ÷ 9 = 40 square yards. Carpet is often priced per square yard.
How do I find the square footage of a circle?
Measure the diameter, halve it to get the radius, square the radius and multiply by π (3.1416). A 12 ft round patio has a 6 ft radius: 3.1416 × 36 = 113.1 ft².
How many square feet are in an acre?
One acre is 43,560 square feet. A 100 ft × 200 ft lot is 20,000 ft², or about 0.46 acres.
Formulas, unit conversions and default values are explained on our methodology page. Results are estimates; check manufacturer data and local codes before you buy or build.