How to calculate square footage
Square footage is area in feet — three formulas cover nearly every room, slab, and yard:
yd² = ft² ÷ 9 · m² = ft² × 0.0929 · acre = 43,560 ft²
Worked example: square footage of an L-shaped room
Split the L into two rectangles: 12 × 10 (120 ft²) and 6 × 4 (24 ft²). Add both to the running total — 144 ft², or 16 yd² for the carpet quote. That's the whole method for a house: rooms in, total out.
Square footage conversions
| Unit | Conversion |
|---|---|
| Square yards (carpet) | ft² ÷ 9 |
| Square meters | ft² × 0.0929 |
| Acres (land) | ft² ÷ 43,560 |
| Squares (roofing) | ft² ÷ 100 |
Square footage FAQ
How do you calculate square footage?
Length × width, both in feet — a 12 × 10 room is 120 ft². Circles are π × (diameter ÷ 2)², triangles are base × height ÷ 2. For L-shaped rooms, split into rectangles and add them — the running total on this page does the adding.
How do I calculate the square footage of a house?
Measure room by room along the floor, including closets and hallways, and add them with the running total. Listing standards (ANSI Z765) measure exterior walls of finished, heated space — so your interior room-by-room total will read slightly smaller than the listed number.
How many square feet are in a square yard?
Nine. Carpet and some concrete flatwork quote in square yards, so divide square feet by 9 — the calculator shows the conversion live. 120 ft² is 13.33 yd².
How many square feet in an acre?
43,560 ft² — a 660 × 66 ft strip, the historic "furlong by a chain." The acres line matters once you're measuring lots rather than rooms.
How do I measure an odd-shaped room?
Break it into shapes you can measure — rectangles first, a triangle for the angled bay, a half-circle if there is one — calculate each, and add every piece to the running total. Overlap nothing, and sketch it as you go.
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