Square Footage Calculator
This square footage calculator measures a room, an irregular space or a whole property, then converts it to square yards, square metres or acres.
Room or Rectangle
Irregular or Multi-Section Space
Split an L-shaped room, a whole floor or an odd garden into rectangles and add them up. Leave unused sections at zero.
Circle or Ring
Round patios, fire pit surrounds, tree rings and circular lawns.
Triangle, Trapezoid or Parallelogram
For corner lots, gable ends and anything that is not a rectangle.
Cost Per Square Foot
Flooring, tile, paint, turf or a build quote, anything priced by the square foot.
Convert an Area
Square feet to acres, square yards or square metres, and back.
How to use the Square Footage Calculator
Measure wall to wall at floor level, not at waist height, walls are rarely parallel and skirting throws the reading off. If a room is out of square, take the longest and widest points, then check a second measurement partway along. Measure into doorways and closets if the flooring runs through them.
Units can be mixed, so 12 ft 6 in goes in as 12.5 feet or as 150 inches, whichever way you wrote it down.
Which tab you want depends on the shape:
- Room or Rectangle, a plain four-walled room. Set Number of Rooms if several are identical.
- L-Shape, split the floor into rectangles, enter each one, and the tab adds them up. Leave the sections you do not need at zero.
- Circle, a round room, patio or pool. The ring option subtracts an inner diameter, which is what you want for a border or a path running round something.
- Other Shapes, triangles, trapezoids and parallelograms, for gable walls, corner cuts and angled bays.
- Cost, the same area maths with a price per square foot and an optional labour rate.
- Convert, turns a figure you already have into square yards, square metres or acres.
The waste allowance is there because flooring and tile get cut to fit. Five per cent covers a straightforward room; ten is nearer the mark for a diagonal or herringbone layout, or a floor with a lot of corners.
Square Footage formula
Square footage is length times width, with both measurements in feet:
square feet = length × width- From inches:
sq ft = (length in × width in) ÷ 144 - Irregular spaces: split into rectangles and add the results
The conversions are exact definitions, not measurements:
| Unit | In square feet |
|---|---|
| 1 square yard | 9 sq ft |
| 1 square metre | 10.7639 sq ft |
| 1 acre | 43,560 sq ft |
| 1 hectare | 107,639 sq ft |
| 1 square mile | 27,878,400 sq ft |
Worked example
An L-shaped living room, 16 ft × 12 ft with an 8 ft × 6 ft alcove:
- Main section: 16 × 12 = 192 sq ft
- Alcove: 8 × 6 = 48 sq ft
- Total: 240 sq ft, about 26.7 square yards
For flooring, add 10 percent for cuts and waste, which takes it to 264 sq ft.
What the result means
What counts as square footage in a house
This is the question that causes arguments, and the US has a standard for it: ANSI Z765, which is what appraisers and most MLS listings follow. The short version:
- Finished, heated, above-grade space counts. That is the headline number on a listing.
- Ceilings must be at least 7 ft (5 ft under a slope, and at least half the floor area must have the full 7 ft).
- Basements do not count in the main figure even when finished, anything below grade is listed separately.
- Garages, unheated porches, attics and sheds are excluded.
- Stairs count once, on the floor they descend from.
- Measured to the outside of exterior walls for the house total, not wall-to-wall inside, which is what you want for flooring.
So the same house has two legitimate different numbers: gross living area for a listing, and interior floor area for buying carpet. Neither is wrong; they answer different questions. This calculator gives you interior area, which is the one you want for materials.
Local practice and appraiser judgement vary, so treat a listing figure as a claim rather than a measurement.
What square footage feeds into
Square footage is the starting point for almost every material estimate, flooring, tile, paint, sod, mulch and concrete all begin here, then get multiplied by a depth or a coverage rate.
What counts as “square footage” depends on who is asking. Estate agents usually quote gross living area measured to the outside of exterior walls and exclude garages and unfinished basements. A flooring contractor measures the actual floor inside the walls. The two numbers for the same house can differ by a lot, and neither is wrong.
Common mistakes
- Mixing feet and inches in one number. 12 ft 6 in is 12.5 ft, not 12.6.
- Measuring only the longest wall. Bays, alcoves, chimney breasts and closets all change the figure. Split and add.
- Forgetting waste on flooring. Planks and tiles are cut to fit, and off-cuts are rarely reusable. Five percent for a simple square room, ten or more for diagonal layouts and patterns.
- Confusing square feet with feet. A 10 × 10 room is 100 square feet, not 20 or 40. Perimeter and area are different questions.
Frequently asked questions
How do I calculate the square footage of a room?
Multiply the length by the width in feet. A room 16 feet by 12 feet is 192 square feet. If the room is not a rectangle, split it into rectangles, work each one out and add them together.
How many square feet are in an acre?
43,560 square feet exactly. It is a defined figure, not a rounded one, an acre was historically one chain by one furlong, which works out to exactly that.
How do I convert square feet to square yards?
Divide by 9, because a square yard is 3 feet by 3 feet. So 240 square feet is 26.67 square yards. Carpet is often priced this way.
How do I calculate square footage of an irregular room?
Break it into rectangles. Draw the room, divide it along the corners into simple boxes, measure each and add the areas. The L-Shape tab does the adding for up to four sections.
Does square footage include walls, closets or the garage?
It depends on the purpose. Property listings usually measure gross living area to the outside of exterior walls, count closets, and exclude garages and unfinished basements. A flooring estimate measures the floor you can actually walk on. Say which one you mean when you quote a figure.
How much flooring waste should I add?
Five percent for a simple rectangular room with a straight layout. Ten percent for rooms with lots of corners, and fifteen for diagonal or herringbone patterns where off-cuts are harder to reuse.
How do I calculate the square footage of a circle?
Multiply pi by the radius squared, the radius being half the diameter. A 12 foot circle is 3.14159 × 6 × 6 = 113.1 square feet. The Circle tab does it, and also handles rings, where you subtract the inner circle from the outer.
How do I calculate the square footage of a triangle?
Half the base times the perpendicular height. If you only have the three side lengths, use Heron’s formula instead, the Other Shapes tab takes either.
Does a basement count in a house’s square footage?
Not in the headline figure, under the ANSI Z765 standard most US appraisers and listings follow. Below-grade space is listed separately even when it is finished and heated. Garages, unheated porches and attics are excluded entirely.
How much extra flooring should I order?
Ten percent over the measured area for straight-laid plank or tile, and fifteen to twenty for diagonal, herringbone or heavily patterned work. Buy it all in one order so the batch matches.
Sources and assumptions
Every figure on this page is exact arithmetic. The unit relationships are definitions: a square yard is exactly 9 square feet, an acre is exactly 43,560 square feet, and the metric conversions derive from the exact 0.3048 metres in a foot.
What varies is not the maths but the convention, which parts of a building count toward its square footage differs between property listings, tax assessments and trade estimates.