Square Footage Calculator

Measure the space with a tape first and write the numbers down. You can enter them in whichever unit your tape uses, because the tool converts everything to feet before it calculates.

1. Pick the Shape: Rectangle or square, Triangle, or Circle (enter the diameter).
2. Choose the unit in Measured in: Feet, Inches, Yards, Metres or Centimetres.
3. Type the Length, base or diameter. Then type the Width or height, a field that disappears for a circle because one measurement is enough.
4. Set How many of this shape if you have several identical areas, and Extra for waste and cuts (%) if you are buying material.
5. Optionally enter the Price per square foot (optional) to get a cost.
6. Read the total area, the total with the waste allowance, and the conversions to square yards, square meters and acres.

The tool uses the standard area formulas. A rectangle is length x width, a triangle is base x height / 2, and a circle is pi x (diameter / 2) squared. A square is just a rectangle with two equal sides.

Take a room that is 12 feet by 15 feet. The area is 12 x 15 = 180 sq ft. Add 10 percent for waste and cuts and you get 180 x 1.10 = 198 sq ft. That total is 22 square yards, 18.395 square meters and 0.00455 acres. At a price of 3.50 per square foot the cost is 198 x 3.50 = 693.00. The cost uses the total with the waste allowance, because that is the amount you actually buy.

Two more checks you can reproduce. A triangle with a base of 10 ft and a height of 8 ft covers 40 sq ft, and a quantity of 2 gives 80 sq ft. A circle with a 4 meter diameter covers 12.566 square meters, which is 135.26 sq ft. The metric figure comes from 1 square foot = 0.09290304 square meters.

The calculator handles one shape type at a time. For an L-shaped room, split it into two rectangles, calculate each and add the results by hand. The quantity box is for identical shapes, such as six equal flower beds, not for different ones. Subtract windows, doors and built-ins yourself when you are working out paint or wallpaper, because the tool does not know about openings. For a quick paint estimate, calculate the floor or wall as a rectangle, then work out the area of each door and window the same way and subtract it by hand.

Tape-measure habits matter more than the arithmetic. Measure at the widest and longest points, take each dimension twice, and write down inches and feet separately before you convert, so that 11 feet 6 inches becomes 11.5 feet and not 11.6.

The waste percentage is your own judgment. Straight layouts normally need less extra than diagonal or patterned ones, and products sold in boxes or rolls round up anyway, so check what the supplier recommends. If you enter 0 the waste row is hidden and the total equals the measured area.

Frequent errors are mixing units, such as a length in feet and a width in inches, entering a circle radius where the diameter belongs (which gives a quarter of the right area), and measuring one wall of a room that is not square. Note that the price field is per square foot even when you measure in meters, so convert a per-square-meter quote first. Divide it by 10.7639 for the per-square-foot figure.

Results are planning estimates and not a substitute for a supplier quote or a professional survey. To convert an area you already know, use the square feet to square meters converter or the area converter, and the acres to square feet converter for land. For a lengths-only conversion, try the length converter, and the percentage increase calculator if you want to check a waste figure.

Land is the same method with bigger numbers. A rectangular lot of 100 ft by 150 ft is 15,000 sq ft, which is 0.344 acres when divided by 43,560. Irregular lots are easiest to handle by splitting them into rectangles and triangles, calculated separately and added together.