About this calculator
Square footage is the area of a floor, wall or lot measured in square feet — the basic number behind flooring, paint, sod, real-estate listings and contractor quotes. This calculator works out the area of a rectangle, a triangle, a circle or a half circle, and combines up to three of them: add pieces for an L-shaped room, a bay or a closet, or subtract pieces for a kitchen island, a fireplace hearth or a missing corner.
Enter measurements in feet, inches, yards, meters or centimeters; results are shown in square feet, square yards, square meters and acres, with each piece listed on its own. The sketch draws every piece to the same scale as you type, so a mistyped 120 ft instead of 12 ft is easy to spot before you buy anything.
How to use it
- Pick the shape of the main area and enter its length and width. For a triangle, the width is the height measured square to the base; for a circle, the length is the diameter.
- If the space isn’t one simple shape, split it into up to three pieces. Set each extra piece to Add it (an L-shaped leg, a bay) or Subtract it (an island, a built-in, a corner that’s missing). Leave unused areas at 0.
- Pick the unit for each measurement from its dropdown — you can mix feet, inches and meters — and check the sketch: each piece should look the way it does on the floor.
- Optionally enter a price per square foot to estimate the cost of flooring, installation or other work on the total area.
The formula
Rectangle = length × width
Triangle = base × height ÷ 2
Circle = π × diameter² ÷ 4 (π × radius²)
Half circle = π × diameter² ÷ 8
Total = added pieces − subtracted pieces
Square yards = square feet ÷ 9 · Square meters = square feet × 0.0929 · Acres = square feet ÷ 43,560
These are the standard area formulas. For a triangle the height must be measured at a right angle to the base, not along a sloping side. For a room with a missing corner, either add two rectangles or enter the full outer rectangle and subtract the missing corner; both give the same answer.
Worked example
These are the calculator’s starting values and the results they produce:
| Area 1 shape | Rectangle |
|---|---|
| Area 1 length | 12 ft |
| Area 1 width | 10 ft |
| Area 2 | Add it |
| Area 2 shape | Rectangle |
| Area 2 length (optional) | 0 ft |
| Area 2 width (optional) | 0 ft |
| Area 3 | Add it |
| Area 3 shape | Rectangle |
| Area 3 length (optional) | 0 ft |
| Area 3 width (optional) | 0 ft |
| Price per square foot (optional) | $0.00 |
Tips before you buy
- Measure to the nearest inch and round up, not down, when you’re buying materials.
- For flooring, include closets and the space under doors; for paint, measure walls instead of floors.
- For flooring, subtract only what the floor won’t run under: floating floors usually stop at cabinets and islands, while tile often runs beneath them. The installation guide says which.
- A laser distance measure makes long rooms and high ceilings a one-person job.
- Real-estate square footage usually counts finished, heated space only; methods vary by region.
Frequently asked questions
How do I calculate square footage?
Multiply the length by the width, both in feet. A room 12 ft long and 10 ft wide is 120 square feet.
How do I calculate the square footage of an L-shaped room?
Split the L into two rectangles, calculate each area and add them. For example, 12 × 10 ft plus 6 × 8 ft is 120 + 48 = 168 sq ft.
How do I find the square footage of a circle or a triangle?
A circle is π × radius²: a circle 10 ft across (5 ft radius) is about 78.5 sq ft. A triangle is base × height ÷ 2: a 12 ft base with an 8 ft height is 48 sq ft.
How do I subtract a kitchen island?
Work out the floor, then take the island away: a 12 × 10 ft kitchen with a 6 × 3 ft island is 120 − 18 = 102 sq ft of open floor.
How do I convert inches to square feet?
Multiply length × width in inches and divide by 144. A 96 × 120 in area is 11,520 sq in ÷ 144 = 80 sq ft.
How many square feet are in a square meter?
One square meter is 10.764 square feet, and one square foot is 0.0929 square meters.
Sources
Areas and volumes are standard geometry. The published figures this calculator relies on come from these sources; other defaults (waste allowances, typical densities and prices) are common trade figures worth checking with your supplier.
- NIST: unit conversion: metric: 1 ft = 0.3048 m exactly, 1 sq ft = 0.0929 m²