How to calculate square footage
Square footage is the area of a flat surface measured in square feet. For a rectangle — which covers most rooms — multiply the length by the width, both in feet.
Triangle: ½ × Base × Height
Circle: π × (Diameter ÷ 2)²
Trapezoid: ½ × (Side a + Side b) × Height
Example: a bedroom measures 12 ft 6 in by 11 ft.
- Convert inches to feet: 6 ÷ 12 = 0.5, so 12 ft 6 in = 12.5 ft
- 12.5 × 11 = 137.5 sq ft
Irregular and L-shaped rooms
Split the space into rectangles (and triangles if there are angled walls), calculate each piece, and add them together. For an L-shaped living room, draw a line that divides it into two rectangles:
Section A: 20 ft × 12 ft = 240 sq ft
Section B: 10 ft × 8 ft = 80 sq ft
Total: 320 sq ft
If there's an area you won't cover — a fireplace hearth or kitchen island — calculate it separately and subtract it. In the calculator, tick "Subtract" on that area.
How to measure a room accurately
- Use a tape measure or laser measure and record measurements to the nearest inch.
- Measure wall to wall at floor level, ignoring baseboards.
- Measure each dimension twice — rooms are rarely perfectly square — and use the larger number when ordering materials.
- Sketch the room and write each measurement on the drawing so you can check it later.
- Include closets and alcoves if the flooring will continue into them.
How much extra material to buy
You'll lose some material to cuts, mistakes and damaged pieces. Add a waste allowance to your square footage before ordering:
| Material / layout | Typical waste allowance |
|---|---|
| Carpet, vinyl sheet | 5%–10% |
| Laminate, vinyl plank, hardwood (straight lay) | 7%–10% |
| Tile (straight lay) | 10% |
| Diagonal or herringbone patterns | 15%–20% |
| Paint (walls) | 1 gallon covers ~350–400 sq ft per coat |
| Sod | 5% |
It's worth keeping one extra box of flooring or tile for future repairs, since dye lots change.
Square footage of a house
For home listings and appraisals, "gross living area" normally counts only finished, heated space that's above grade. The ANSI Z765 standard, widely used in the US, measures from the exterior walls and excludes garages, unfinished basements, porches and areas with ceilings under 7 feet. Finished basements are usually listed separately. That's why the square footage on a listing rarely equals the sum of the room sizes you measure inside.
Area conversion table
| From | To | Multiply by |
|---|---|---|
| Square feet | Square meters | 0.092903 |
| Square meters | Square feet | 10.7639 |
| Square feet | Square yards | 0.11111 (÷ 9) |
| Square inches | Square feet | 0.006944 (÷ 144) |
| Acres | Square feet | 43,560 |
Ordering gravel, mulch or concrete? Those are sold by volume, so use the gravel calculator to turn square footage and depth into cubic yards and tons. For roofs, use the roof pitch calculator, which accounts for the slope.
Frequently asked questions
How do I calculate square feet?
Multiply the length by the width, both measured in feet. A 15 ft × 12 ft room is 180 square feet.
How do I calculate square feet from inches?
Multiply length by width in inches, then divide by 144. For example, 96 in × 60 in = 5,760 sq in ÷ 144 = 40 sq ft.
How many square feet is a 12x12 room?
144 square feet.
How do I convert square meters to square feet?
Multiply by 10.7639. A 20 m² room is about 215.3 sq ft.
How many square feet are in an acre?
43,560 square feet — roughly the area of 16 tennis courts or three-quarters of an American football field.