How to use the square footage calculator
- Choose the unit you measured in: feet, inches, yards or meters. All dimensions are converted to feet.
- Add one row per area. Pick its shape (rectangle, triangle, circle or trapezoid) and enter the dimensions that shape needs.
- Mark any row you want to take out, such as a stairwell, fireplace or built-in, as Subtract.
- Read the total in square feet, square yards and square meters. Add a waste allowance and a price per square foot if you are buying material by area.
Formula
Rectangle = length x width
Triangle = base x height / 2
Circle = 3.14159 x (diameter / 2)^2
Trapezoid = (first side + second side) / 2 x height
Net area = sum of added areas - sum of subtracted areas
Square yards = square feet / 9; square meters = square feet x 0.09290304
The circle row asks for a diameter because that is what you can measure across a round room or tub. The trapezoid needs two parallel sides and the distance between them.
Worked example: two rooms with a hearth cutout
A living room 20 ft by 15 ft is 20 x 15 = 300 sq ft. A bedroom 14 ft by 12 ft is 14 x 12 = 168 sq ft.
A raised hearth 4 ft by 2 ft is 8 sq ft that you will not floor, so it is subtracted.
Net area = 300 + 168 - 8 = 460 sq ft. That is 460 / 9 = 51.11 square yards, or 460 x 0.09290304 = 42.74 square meters.
With a 10% waste allowance you would buy for 506 sq ft. At $2.50 per square foot the material costs $1,150.00 for the measured area and $1,265.00 with waste.
Breaking a room into shapes
Most floor plans are not a single rectangle. An L-shaped room is two rectangles, a bay window is often a trapezoid or a half circle and a corner cut at an angle is a triangle. Measure each piece on its own, add them together and subtract anything that will not receive the material, such as a kitchen island base or a built-in cabinet.
Measure at the widest point of each piece and write the numbers down before you enter them. If a wall is not square, take the length at both ends and use the trapezoid shape with the distance between the two walls as the height.
Square feet, square yards and square meters
Carpet is often priced per square yard, listings and appraisals use square feet and international product data often uses square meters. This tool shows all three from the same total so you can compare quotes without converting by hand.
Square footage for a sales listing follows its own rules about which spaces count, and those rules differ by region and by lender. This calculator measures the area you enter and does not decide what counts as living space.
Using the total for other projects
Once you have the area, feed it into a material tool. The flooring calculator turns square feet into boxes, the paint calculator works from wall area and the tile calculator accounts for tile size and grout joints.
Assumptions and limits
- Every shape is treated as flat and exactly as described. Slopes, curves that are not true circles and uneven walls are not modeled.
- Circle rows use the diameter you enter. Trapezoid rows need both parallel sides and the height between them.
- The waste allowance and price per square foot are optional and only change the material lines, never the measured area.
- Rounding is to two decimal places for display. Underlying math keeps full precision.
- This tool measures area only. It does not decide what counts as finished living space for a listing, appraisal or tax purpose.
Frequently asked questions
How do I calculate the square footage of an L-shaped room?
Split the L into two rectangles, enter each as its own row and let the tool add them. If the overlap is counted twice, mark the overlap as a subtract row.
How many square feet are in a square yard?
There are 9 square feet in a square yard because a yard is 3 feet on each side and 3 x 3 = 9. The tool divides your total by 9 to show square yards.
Can I measure a round room or a circular patio?
Yes. Pick the circle shape and enter the diameter, which is the distance straight across through the center. The tool uses pi times the radius squared.
What should I subtract from a room measurement?
Subtract areas that will not get the material you are buying, such as a stairwell opening, fireplace hearth or fixed cabinet base. Leave out doorways because flooring usually runs through them.
Why is there a waste allowance on an area tool?
Area is what you measure, but material is bought with extra for cuts and mistakes. The allowance shows the larger figure you would buy without changing the measured total.