Square Footage Calculator
Add rectangles, L-shapes, circles, triangles and trapezoids, subtract cut-outs, and get square feet, square metres, yards and acres with a total cost.
The interactive tool loads here when JavaScript runs.
About this toolWhat is the Square Footage Calculator?
Few rooms are a single rectangle. Kitchens have an island cut out of the floor, living rooms open into a bay window, and gardens bend around a path. This square footage calculator lets you describe a space as a list of simple pieces, add the ones that are floor and subtract the ones that are not, and see the total in square feet, square metres, square yards, acres and hectares at the same time.
Each section can be a rectangle, an L-shape split into two rectangles, a circle by diameter, a triangle by base and height, or a trapezoid. Every row shows its own area so you can check the pieces against a sketch, and the total updates as you type. Measurements can be in feet, inches, yards, metres or centimetres.
Below the total, a price panel multiplies the area by a cost per square foot, square yard or square metre, with an optional waste allowance for flooring, sod or paint coverage. Carpet is often priced by the square yard and tile by the square foot, so the unit is selectable.
- Five shapes per section: rectangle, L-shape, circle, triangle and trapezoid
- Unlimited add and subtract rows (up to 20) with a running area per row
- Results in ft², m², yd², in², acres and hectares at once
- Cost by ft², yd² or m² with an optional waste percentage
- Shareable link that reopens every section exactly as entered
How to use the Square Footage Calculator
- Pick the unit you measured in. All sections use the same unit.
- Describe the first section: choose its shape and enter its dimensions. Its area appears under the fields.
- Add more sections for alcoves, extensions or separate rooms. Set any section to Subtracting for islands, columns, fireplaces or other areas you will not cover.
- Read the total in square feet, square metres, square yards and acres, plus the conversion table.
- Enter a price per unit area and a waste percentage to estimate material cost, then copy or share the breakdown.
Worked examples
Open-plan room with a kitchen island
Input
Rectangle 12 x 15 ft, plus rectangle 8 x 10 ft, minus 3 x 4 ft island
Output
248 ft² = 23.04 m² = 27.56 yd²; at 4.50 per ft² the cost is 1,116.00
This is the default example. The island is subtracted because flooring goes around it, not under it.
A circular patio
Input
Circle, diameter 12 ft
Output
113.10 ft² (10.51 m²)
Area is pi times the radius squared. Doubling the diameter quadruples the area, which surprises people pricing a larger patio.
Is this lot an acre?
Input
Rectangle 150 x 290 ft
Output
43,500 ft² = 0.9986 acres
Just short of the 43,560 ft² acre. A listing that rounds this up to one acre is close but not exact.
Background and insight
Square footage is a measure of area: length times width for a rectangle. The trap is the unit change. A square foot is 0.09290304 square metres exactly, because the international foot has been defined as 0.3048 m since 1959, but a square yard is 9 square feet, not 3, and an acre is 43,560 square feet. Converting a length and then squaring is safe; converting an area by the length factor is the error that produces a quote three times too small.
Splitting irregular shapes into rectangles and triangles is the same method surveyors use for plan areas, and it is exact as long as the pieces do not overlap. When they do, subtract the overlap or measure the pieces differently. For a home appraisal or listing, the gross living area follows local or ANSI Z765 rules about walls, stairs and ceiling height, which this calculator does not apply; it measures whatever you describe.
Common use cases
Flooring and carpet
Measure every room and closet as separate sections, subtract fixed cabinets, and price the total with a waste allowance.
Painting and wall coverings
Treat each wall as a rectangle and subtract windows and doors to estimate paint or wallpaper coverage.
Sod, seed and landscaping
Combine curved beds (circles and trapezoids) and lawns, then convert to square yards or acres for supplier quotes.
Rent and real-estate checks
Sanity-check a listed square footage or compare price per square foot between properties.
Tips and limitations
- Measure to the wall, not the baseboard, and round each dimension up to the next inch. Small rounding errors add up across several rooms.
- Draw the room first and split it so no two pieces overlap. An L-shape is two rectangles that meet along one edge, not two that both include the corner.
- Add 5 to 10% waste for flooring laid straight and 15% or more for diagonal patterns or rooms with many corners.
- Carpet is sold by width off a roll, so the amount you buy depends on seams as well as area. Use the result as a floor, not a final order.
- If the total goes negative, a section meant to add is set to subtract.
Frequently asked questions
How do I calculate the square footage of an L-shaped room?
Split the L into two rectangles that do not overlap, multiply length by width for each, and add them. A room made of a 20 x 10 ft part and an 8 x 6 ft part is 200 + 48 = 248 ft². Choose the L-shape option to enter both parts in one section.
Is a lot of 150 by 290 feet a full acre?
Almost: 150 x 290 = 43,500 ft², or 0.9986 acres. An acre is exactly 43,560 square feet, which is 4,046.86 square metres or about 0.405 hectares. A square plot of one acre is about 208.7 feet on each side.
How do I convert square feet to square metres?
Multiply by 0.09290304, or divide by about 10.764. So 248 ft² is 23.04 m². Do not divide by 3.28; that factor converts lengths, and areas need it squared.
How do I convert square feet to square yards for carpet?
Divide by 9, because a yard is 3 feet and 3 x 3 = 9. A 12 x 15 ft room is 180 ft², which is 20 square yards.
Should I subtract closets and kitchen islands when measuring a floor?
Subtract anything the material will not go under, such as fixed islands, built-in cabinets and fireplaces. Closets usually get the same flooring, so add them as their own sections.
How do I find the area of a room with a bay window or angled wall?
Measure the main rectangle, then add the bay as a trapezoid (two parallel sides and the depth) or a triangle. Splitting odd shapes into pieces you can measure is exact as long as the pieces do not overlap.
Is there an in-depth guide to the Square Footage Calculator?
Yes. “Estimating Concrete, Flooring, Tile and Gravel Without Running Short” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
Related Tools You May Like
Free, in-browser tools that pair well with this one.