Square footage is the starting point for nearly every material estimate — flooring, paint, tile, drywall, sod. This calculator handles rectangles, circles, triangles, and L-shaped rooms, and lets you add multiple areas together with a waste allowance.
Need to convert that area into a length of material? See Square Feet to Linear Feet.
About pricing on this page
This calculator is intentionally price-light. Absolute dollar figures are deliberately omitted because they vary too widely by region, brand, and installer to be useful as planning estimates. The relative-comparison tables below show how options stack up against each other — which is the durable, actionable information. For a real budget, get two or three written quotes from local suppliers and contractors after they have seen the job.
Square Footage Calculator
Choose a shape, enter dimensions in feet or inches, and get square footage with optional waste allowance.
Square Footage Formulas by Shape
| Shape | Formula | Example | Result |
|---|---|---|---|
| Rectangle / square | Length × Width | 12 ft × 10 ft | 120 sq ft |
| Triangle | (Base × Height) ÷ 2 | 10 ft × 8 ft ÷ 2 | 40 sq ft |
| Circle | 3.1416 × Radius² | Radius 6 ft | 113 sq ft |
| Trapezoid | ((Side A + Side B) ÷ 2) × Height | (10 + 14) ÷ 2 × 8 | 96 sq ft |
| L-shape | Rect 1 + Rect 2 | (12×10) + (6×8) | 168 sq ft |
| Wall area | Perimeter × Height | 44 ft × 8 ft | 352 sq ft |
For a rectangular room, perimeter is (length + width) × 2. Perimeter is what drives baseboard, crown molding, and wall paint estimates.
Square Footage Unit Conversions
| Conversion | Multiply / Divide By | Example |
|---|---|---|
| Square inches → square feet | ÷ 144 | 1,800 sq in = 12.5 sq ft |
| Square feet → square yards | ÷ 9 | 180 sq ft = 20 sq yd |
| Square feet → square meters | × 0.0929 | 1,000 sq ft = 92.9 sq m |
| Square meters → square feet | × 10.764 | 100 sq m = 1,076 sq ft |
| Square feet → acres | ÷ 43,560 | 21,780 sq ft = 0.5 acre |
| Acres → square feet | × 43,560 | 2 acres = 87,120 sq ft |
| Square feet → roofing squares | ÷ 100 | 2,400 sq ft = 24 squares |
Square Footage of Common Room Sizes
| Room Size | Square Feet | Perimeter (LF) | Wall Area (8 ft) | Flooring +10% | Typical Room |
|---|---|---|---|---|---|
| 8 × 10 ft | 80 | 36 | 288 | 88 | Small bedroom, office |
| 10 × 10 ft | 100 | 40 | 320 | 110 | Bedroom, dining nook |
| 10 × 12 ft | 120 | 44 | 352 | 132 | Standard bedroom |
| 12 × 12 ft | 144 | 48 | 384 | 158 | Bedroom, small living |
| 12 × 14 ft | 168 | 52 | 416 | 185 | Master bedroom |
| 12 × 16 ft | 192 | 56 | 448 | 211 | Living room |
| 14 × 20 ft | 280 | 68 | 544 | 308 | Large living room |
| 20 × 20 ft | 400 | 80 | 640 | 440 | Two-car garage |
| 24 × 24 ft | 576 | 96 | 768 | 634 | Large garage, great room |
How to Measure a Room Accurately
Measure at Floor Level, Wall to Wall
Take measurements along the floor to the interior face of each wall, not at counter height or across a window sill. Walls are rarely perfectly plumb, and a measurement taken at chest height can differ from the floor dimension by an inch or more over a long wall. For flooring, the floor-level dimension is the one that matters.
Convert Inches to Decimal Feet
A room measuring 12 ft 7 in is 12.583 ft, not 12.7 ft. Divide the inches by 12 to get the decimal: 7 ÷ 12 = 0.583. Treating inches as tenths is a common error that compounds across both dimensions — on a 12 ft 7 in by 10 ft 8 in room it produces an answer about 2% off, which matters on a large flooring order.
Break Irregular Rooms Into Rectangles
For an L-shaped room, extend the line of the inside corner across the space to split the floor into two rectangles. Measure each separately and add the areas. This is more accurate and far faster than trying to treat the whole footprint as a single complex shape, and it gives you a sketch you can hand to a supplier.
Measure Closets and Alcoves Separately
Closet floors, bay window bumpouts, and door alcoves are usually flooring surfaces too, but they fall outside the main rectangle. Each one is a small rectangle to measure and add. A walk-in closet can easily add 30–40 sq ft, which is a full box of tile or a plank carton that would otherwise be missing from the order.
Confusing Square Feet With Linear Feet
These answer different questions and cannot be substituted. Square footage tells you how much surface to cover — flooring, paint, tile. Linear footage tells you how much length to buy — baseboard, trim, gutters, fence. A 12 × 10 room needs 120 sq ft of flooring and 44 linear feet of baseboard, and neither number helps you order the other material.
Dividing by 12 Instead of 144 for Square Inches
Converting square inches to square feet requires dividing by 144, not 12, because both dimensions are being converted. A square foot is 12 in × 12 in = 144 square inches. Using 12 overstates the area by a factor of twelve, which is the same class of error as forgetting to convert depth in a volume calculation.
Ordering Flooring at Exact Square Footage
Every flooring material needs a waste allowance for cuts at walls, around door jambs, and at transitions. Ten percent is standard for a straight layout in a simple room, fifteen for diagonal installs or rooms with many angles. Ordering exactly 168 sq ft for a 168 sq ft room guarantees a second trip, and the replacement material may come from a different production lot.
Using Listed Home Square Footage for Material Orders
The square footage on a real estate listing is gross living area measured to exterior walls, and it includes hallways, stairwells, and wall thicknesses. It is 10–15% larger than the sum of the actual floor surfaces you would install material on. Always measure the rooms you are working in rather than working backward from a listing figure.