Square Footage Calculator
Square feet, square yards, square metres and acres for one shape or up to six added together, with cut-outs subtracted.
The working
Area = Length × Width
= 12 ft × 12 ft
= 144 ft²
Square yards = Square feet ÷ 9
= 144 ÷ 9
= 16 yd²
Square metres = Square feet × 0.09290304
= 144 × 0.09290304
= 13.38 m²
Acres = Square feet ÷ 43,560
= 144 ÷ 43,560
= 0.0033 acres
Square inches = Square feet × 144
= 144 × 144
= 20,736 in²
Total area
square feet
- Square yards
- 16yd²
- Square metres
- 13.38m²
- Acres
- 0.0033acre
- Square inches
- 20,736in²
Pick a shape and enter its dimensions in any unit: feet, inches, yards, metres or centimetres, each field on its own. For an L-shaped room, a floor made of several rooms or a yard with a pool in it, add up to six areas and set the cut-outs to Subtract. Everything is converted to feet first, and every step of the arithmetic is shown with the answer.
How this calculator works
Only your inputs and exact unit conversions. Where a figure comes from anywhere else, it is recorded below with its source.
- Formula version
- 1.0.0
- Last reviewed
- 2026-09-29
- External data
- None
- Category
- Measurement
What this calculates
The plan area of flat surfaces: a floor, a patio, a yard, a lot. Choose a shape and enter its dimensions. The calculator returns square feet, with square yards, square metres, acres and square inches beside it.
For a space made of several parts, set Number of areas as high as six. Each area has its own shape and its own units. From the second area on, each one can be added to the total or subtracted from it.
How to calculate square footage
Multiply the length by the width, both in feet. A room 12 ft by 15 ft is 12 × 15 = 180 sq ft.
Convert a measurement to feet first: divide inches by 12, multiply yards by 3, divide metres by 0.3048 and centimetres by 30.48. The calculator does this for each field separately, so every length can be in a different unit.
The formula for each shape
Three sides make a triangle only when the longest is shorter than the other two together. If they do not, the calculator says so rather than giving a number. It works Heron’s formula in an algebraically equivalent arrangement, with the sides sorted longest first, which stays accurate for long, thin triangles.
- Rectangle: Length × Width.
- L-shape: Overall length × Overall width − Missing corner length × Missing corner width.
- Circle: π × Diameter² ÷ 4. A 12 ft circle is π × 144 ÷ 4 = 113.1 sq ft. For a radius, the diameter is twice it.
- Triangle: Base × Height ÷ 2, with the height at right angles to the base. 10 ft × 8 ft ÷ 2 = 40 sq ft.
- Triangle from three sides (Heron’s formula): s = (a + b + c) ÷ 2, then Area = √(s × (s − a) × (s − b) × (s − c)). Sides of 9, 12 and 15 ft give s = 18 and √(18 × 9 × 6 × 3) = 54 sq ft.
- Trapezoid: (Parallel side 1 + Parallel side 2) ÷ 2 × Height, with the height measured at right angles between the parallel sides. (10 + 14) ÷ 2 × 6 = 72 sq ft.
- Known area: used as entered, after conversion to square feet.
L-shaped and irregular spaces
An L-shaped room can be measured two ways, and both give the same area. Take the overall rectangle and subtract the missing corner: 20 ft × 16 ft − 8 ft × 6 ft = 320 − 48 = 272 sq ft. Or split it into two rectangles that do not overlap: a full-length strip, 20 ft × 10 ft, plus the part beside the corner, 12 ft × 6 ft, is 200 + 72 = 272 sq ft. The calculator uses the first way and prints the second as a check.
Any other irregular space works the same way. Split it into rectangles, triangles, trapezoids and circles, one per area, and set an island, a hearth, a column or a pool to Subtract. A curved edge has to be approximated with one of these shapes.
Feet and inches, and mixed units
Each length has its own unit select: feet, inches, yards, metres or centimetres. A field holds one number, so a measurement in feet and inches goes in as total inches or as decimal feet. 12 ft 6 in is 12 × 12 + 6 = 150 in, or 12.5 ft, because 6 ÷ 12 = 0.5.
A room 11 ft 8 in by 13 ft 9 in is 140 in by 165 in. 140 × 165 = 23,100 sq in, and 23,100 ÷ 144 = 160.42 sq ft. Typing 11.67 ft rounds the 8 inches; entering the lengths in inches keeps the result exact.
Square yards, square metres and acres
Each conversion is exact and follows from a definition. 1 yd = 3 ft, so 1 sq yd = 9 sq ft: divide square feet by 9. 1 ft = 0.3048 m exactly, so 1 sq ft = 0.3048² = 0.09290304 m²: multiply square feet by 0.09290304. An acre is 43,560 sq ft by definition: divide square feet by 43,560. 1 ft = 12 in, so 1 sq ft = 144 sq in.
A known area can also be entered in hectares, where 1 ha = 10,000 m².
Waste and price
Both are optional and blank until you fill them in. No allowance or price is assumed, because both depend on the material, the layout and the supplier.
With an allowance, the area with it is Total × (1 + allowance ÷ 100). With a price per square foot, square yard or square metre, the material cost is that price times the area, including your allowance if you entered one. The working shows the cost three ways, the area in sq ft, sq yd and m² times the price in the same unit, so the line in the unit you priced in uses your price exactly as typed.
From area to volume
Square footage is often the first step toward a volume. Cubic yards = square feet × depth in feet ÷ 27, or square feet × depth in inches ÷ 324, because 27 × 12 = 324. A 144 sq ft area 4 in deep is 144 × 4 ÷ 324 = 1.78 cu yd.
The cubic yard calculator does this in its Area × depth mode, and the asphalt calculator takes a known area. The concrete, gravel, topsoil and soil calculators take the dimensions directly.
An L-shaped living room and a hallway, minus a hearth
Three areas with mixed units: the living room in feet, the hallway’s width in inches, and the hearth in inches, set to Subtract.
- Area 1, L-shape
- 20 ft × 16 ft, missing an 8 ft × 6 ft corner
- Area 2, hallway
- 12 ft × 42 in
- Area 3, hearth (subtract)
- 60 in × 20 in
- 01Area 1, overall minus the corner= 20 × 16 − 8 × 6 = 320 − 48= 272 sq ft
- 02Area 2, the width in feet= 42 in ÷ 12= 3.5 ft
- 03Area 2= 12 ft × 3.5 ft= 42 sq ft
- 04Area 3, square inches to square feet= 60 × 20 = 1,200 sq in ÷ 144= 8.33 sq ft
- 05Total= 272 + 42 − 8.33= 305.67 sq ft
- 06Square yards and square metres= 305.67 ÷ 9 and 305.67 × 0.09290304= 33.96 sq yd and 28.4 m²
305.67 sq ft (0.007 acres)
Square footage by room dimensions
Dimensions in feet. Each row is length × width, then ÷ 9 for square yards and × 0.09290304 for square metres, rounded to two decimals, so any row can be checked by hand.
| Dimensions | Square feet | Square yards | Square metres |
|---|---|---|---|
| 8 ft × 8 ft | 64 | 7.11 | 5.95 |
| 12 ft × 8 ft | 96 | 10.67 | 8.92 |
| 10 ft × 10 ft | 100 | 11.11 | 9.29 |
| 10 ft × 12 ft | 120 | 13.33 | 11.15 |
| 12 ft × 12 ft | 144 | 16 | 13.38 |
| 12 ft × 15 ft | 180 | 20 | 16.72 |
| 20 ft × 20 ft | 400 | 44.44 | 37.16 |
| 24 ft × 24 ft | 576 | 64 | 53.51 |
| 30 ft × 50 ft | 1,500 | 166.67 | 139.35 |
Geometry only: the area of a rectangle with these dimensions. For your own room, enter what you measure.
What it assumes
- 01Surfaces are flat and level, and measured in plan.
- 02Corners are right angles where a shape needs them: a rectangle’s corners, and the height of a triangle or a trapezoid.
- 03Separate areas do not overlap. An overlap is counted twice.
- 04Each subtracted area lies inside an area you added. The calculator cannot check this.
- 05Every conversion is exact and definitional.
- 06Waste and price are used only if you enter them.
What it does not do
- A sloped surface, such as a roof or a bank, has more surface than its plan area, and a roof’s area is not the footprint of the building under it.
- Curved or irregular edges have to be approximated with the shapes offered.
- Six areas per run. For more, work out a subtotal and enter it as a Known area.
- It gives no box, carton, roll or coverage counts. Those depend on the product, and no product data is built in.
- It is not an appraisal or listing measurement. For single-family homes on loans sold to Fannie Mae (attached or detached, including townhomes, rowhouses and manufactured homes), appraisers must follow the ANSI Z765-2021 square footage standard when measuring, calculating and reporting above- and below-grade square footage. An apartment unit in a condo or co-op project is measured by interior perimeter instead, and a state law or regulation can require a different standard (Fannie Mae Selling Guide B4-1.3-05, version dated 06/04/2025, read 2026-09-29). This tool applies none of those rules.
Common questions.
- How do I calculate square footage?
- Measure the length and the width in feet and multiply them. A room 12 ft by 15 ft is 12 × 15 = 180 square feet. If a measurement is in inches, divide it by 12 first; if it is in metres, divide it by 0.3048. For another shape, use that shape’s formula; for an irregular space, split it into shapes and add them up.
- How many square feet is a 12x12 room?
- 12 × 12 = 144 square feet. That is 16 square yards (144 ÷ 9) and 13.38 square metres (144 × 0.09290304).
- How many square feet are 8x8, 10x10, 20x20 and 30x50?
- 8 × 8 = 64, 10 × 10 = 100, 20 × 20 = 400 and 30 × 50 = 1,500 square feet, with the dimensions in feet. The table above gives these and a few more in square yards and square metres too.
- How do I calculate the square footage of an L-shaped room?
- Take the overall rectangle and subtract the missing corner, or split the L into two rectangles that do not overlap and add them. For an L 20 ft by 16 ft overall with an 8 ft by 6 ft corner missing: 20 × 16 − 8 × 6 = 272 sq ft, or 20 × 10 + 12 × 6 = 200 + 72 = 272 sq ft. Choose L-shape in the calculator and it shows both.
- How do I calculate square footage with feet and inches?
- Turn each measurement into inches or into decimal feet first. 11 ft 8 in is 140 in, and 13 ft 9 in is 165 in. 140 × 165 = 23,100 square inches, and 23,100 ÷ 144 = 160.42 square feet. In the calculator, choose “in” beside the field and type the total inches; each field has its own unit.
- How do I add up several rooms or an irregular shape?
- Split the space into simple shapes: rectangles, L-shapes, triangles, trapezoids and circles. Set Number of areas to how many you have, up to six, and enter each one. Anything inside that is not part of the floor, such as a kitchen island, a hearth or a column, goes in as another area set to Subtract.
- How do I convert square feet to square yards, square metres or acres?
- Divide by 9 for square yards, multiply by 0.09290304 for square metres, and divide by 43,560 for acres. 1,000 sq ft is 111.11 sq yd, 92.9 m² and 0.023 acres. Each factor follows from a definition: a yard is 3 ft, a foot is 0.3048 m exactly, and an acre is 43,560 sq ft.
- How many square feet are in an acre?
- 43,560, by definition. A lot 100 ft by 150 ft is 15,000 sq ft, and 15,000 ÷ 43,560 = 0.3444 acres.
- Is a house’s square footage the sum of its rooms?
- No. Rooms measured from the inside leave out the floor under the walls, and the figure on a listing or an appraisal follows its own rules about what counts, so the sum of the rooms is not the house’s square footage. On those rules: for a single-family home on a loan sold to Fannie Mae, appraisers must follow the ANSI Z765-2021 square footage standard (Fannie Mae Selling Guide B4-1.3-05). This calculator does not apply that standard.
- How much should I add for waste?
- There is no single figure. It depends on the material, the size of the pieces and the layout, so ask your supplier or installer. Enter your own allowance under Waste and price and the calculator adds it; nothing is added until you do.
- How do I get from square feet to cubic yards?
- Add a depth. Cubic yards = square feet × depth in inches ÷ 324 (or × depth in feet ÷ 27). A 144 sq ft area 4 in deep is 144 × 4 ÷ 324 = 1.78 cubic yards. The cubic yard calculator does this in its Area × depth mode.
Where people go next
Ordered by what usually comes next in the same job, not by keyword.