How to use the square footage calculator
- Pick a shape for the first area: rectangle, circle, triangle or ring.
- Enter the dimensions in feet, or type feet and inches directly, like
12'6",12ft 6inor12-6. - Have a closet, island or stairwell to leave out? Press Subtract a cut-out and enter its length and width.
- Press Add another area for every other room or section — an L-shaped room is just two rectangles added together.
- Optional: enter a price per square foot and a waste allowance for flooring, sod or paint, and read the total to buy and its cost.
- Read the result in square feet, square yards, square metres and acres.
How to calculate square footage
Square footage = length × width, both measured in feet. A room 12 ft by 10 ft is 12 × 10 = 120 sq ft.
Other common shapes:
- Circle (round patio, fire pit): π × (diameter ÷ 2)². A 12 ft diameter circle = 113.1 sq ft.
- Triangle (gable end, triangular bed): base × height ÷ 2. A 20 ft base, 8 ft height triangle = 80 sq ft.
- Ring (border around a round bed): π × [(outer ÷ 2)² − (inner ÷ 2)²]. A 10 ft outer, 4 ft inner ring = 66 sq ft.
L-shaped and irregular rooms
Split the floor plan into simple rectangles, work out each one, then add the totals. Here's a room made of two rectangles:
16 ft × 12 ft = 192 sq ft, plus 8 ft × 6 ft = 48 sq ft, for a total of 240 sq ft. Press "Add another area" once for each rectangle.
Subtracting cut-outs (islands, closets, stairwells)
A room's usable floor area is often smaller than its outer footprint. A 20 ft × 15 ft kitchen (300 sq ft) with a 4 ft × 4 ft island cut out loses 16 sq ft, leaving 284 sq ft of open floor. This matters most for flooring and paint, where you don't buy material for the island or a built-in closet.
Feet and inches
Tape measures read in feet and inches, not decimal feet, so every length field also accepts feet-and-inches notation: 12'6", 12ft 6in or the shorthand 12-6 all mean 12 feet 6 inches (12.5 ft). A room measuring 12'6" by 10'3" is 12.5 × 10.25 = 128.1 sq ft.
Square feet, square yards, square metres and acres
Multiply or divide from square feet: ÷ 9 for square yards, ÷ 10.764 for square metres, ÷ 43,560 for acres. A 150 ft × 100 ft lot is 15,000 sq ft, which is 1666.7 sq yd, 1393.5 sq m, or 0.344 acres.
Square footage for flooring, with a waste allowance
Flooring, tile and carpet are sold with some allowance for cuts, offcuts and pattern matching — typically 5–10% for a straight lay, more for diagonal patterns or large-format tile. Two rooms totalling 258 sq ft need about 284 sq ft of material with a 10% allowance, or about $993.30 at $3.50 a square foot installed.
Square footage calculator vs concrete calculator
This calculator gives you flat area in square feet — for flooring, paint, sod or a lot size. If you need volume for a concrete pour (a slab needs a thickness too), use the concrete calculator instead.
Related home & garden tools
- Pouring a slab or patio? The concrete calculator adds a thickness and works out cubic yards and bags.
- New beds or a border? The gravel calculator, mulch calculator and topsoil calculator turn an area into cubic yards of material.
Frequently asked questions
How do I calculate square footage?
For a rectangular room, multiply the length by the width, both in feet. A room 12 ft by 10 ft is 120 square feet. For other shapes: a circle is π × (diameter ÷ 2)², a triangle is base × height ÷ 2, and an L-shaped room is two or more rectangles added together.
How do I calculate the square footage of an L-shaped room?
Split it into rectangles, work out each one, then add them together. A room made of a 16 ft × 12 ft section plus an 8 ft × 6 ft section is 192 + 48 = 240 sq ft. Use "Add another area" for each rectangle.
How do I subtract an island, closet or stairwell from a room?
Add the cut-out's own length and width under "Subtract a cut-out" and it's taken off that area's total. A 20 ft × 15 ft kitchen (300 sq ft) with a 4 ft × 4 ft island cut out (16 sq ft) comes to 284 sq ft of usable floor.
How do I enter feet and inches, like 12 feet 6 inches?
Type it straight into a feet field as 12'6", 12ft 6in or 12-6 — all three are read as 12.5 feet. A room 12'6" by 10'3" is 12.5 × 10.25 = 128.1 sq ft.
What is the square footage of a circle, like a round patio?
Square footage = π × (diameter ÷ 2)². A 12 ft diameter circle is 113.1 sq ft. Measure across the middle for the diameter, not the radius.
How do I convert square feet to square yards, square metres or acres?
Divide by 9 for square yards, by about 10.764 for square metres, or by 43,560 for acres. A 150 ft × 100 ft lot is 15,000 sq ft, which is 1666.7 sq yd, 1393.5 sq m, or 0.344 acres.
How much flooring do I need for the square footage of a room?
Add up the room area, then add a waste allowance — typically 5–10% for straight-lay flooring, more for diagonal layouts or patterns that need matching. Two rooms totalling 258 sq ft need about 284 sq ft of material with a 10% allowance, which is roughly $993.30 at $3.50 a square foot installed.
How do I calculate square footage of a triangular space, like a gable end or a triangular yard?
Square footage = base × height ÷ 2. A triangle with a 20 ft base and 8 ft height is 80 sq ft. Height is measured at a right angle to the base, not along a sloped side.
How do I calculate the square footage of a ring-shaped area, like a border around a round bed?
Square footage = π × [(outer diameter ÷ 2)² − (inner diameter ÷ 2)²]. A border with a 10 ft outer diameter and a 4 ft diameter bed inside it covers 66 sq ft.
Why does Google show its own calculator, and is this one different?
Google's AI Overview includes a simple built-in area calculator for quick single-shape questions. This calculator goes further: it adds up several rooms or areas in one total, subtracts cut-outs like islands and closets, accepts feet-and-inches entry, and works out a flooring waste allowance and material cost — the kind of room-by-room job a single quick calculation can't handle.