Quick answer: Square footage = length × width, both in feet. A 12 ft × 16 ft room is 192 sq ft. For odd shapes, split the room into rectangles, triangles and circles, add them up, then add 10 to 20% for wastage before you order.
How square footage is calculated
area = length × width12 ft × 16 ft = 192 sq ftIf your tape reads inches, convert each measurement to feet first by dividing by 12. A room of 150 in × 192 in is 12.5 ft × 16 ft, which is 200 sq ft. Converting after you multiply gives an answer off by a factor of 144.
Rooms that are not rectangles
- L-shaped room: split into two rectangles at the inside corner.
- Alcove or bay: measure it as its own small rectangle.
- Angled corner: a triangle, ½ × base × height. A 3 ft × 4 ft corner is 6 sq ft.
- Round area: π × radius². A 10 ft circle is about 78.5 sq ft.
An L-shaped living room
- Main area: 14 × 20 = 280 sq ft
- Extension: 8 × 6 = 48 sq ft
- Total: 280 + 48 = 328 sq ft
- With 10% wastage: 328 × 1.10 = 360.8 sq ft
Result: order about 361 sq ft
How much extra to order for wastage
| Installation | Allowance | Why |
|---|---|---|
| Straight lay, simple room | 10% | Standard offcuts and trimming |
| Diagonal or herringbone | 15% | Angled cuts waste more at every edge |
| Patterned carpet or tile | 20% | Pattern must line up across seams |
| Many corners or doorways | +5% | Each obstacle adds cuts |
Batches and dye lots also change, so a spare box is cheap insurance if a board or tile needs replacing years later.
Do not subtract furniture: Flooring runs under sofas and kitchen islands, so measure the room as if it were empty.
Converting between square units
| From | To square feet | Multiply by |
|---|---|---|
| 1 square metre | 10.764 sq ft | 10.764 |
| 1 square yard | 9 sq ft | 9 |
| 1 acre | 43,560 sq ft | 43,560 |
| 1 square inch | 0.00694 sq ft | ÷ 144 |
Square units scale in two directions, so there are 9 sq ft in a square yard (3 × 3) and 144 sq in in a square foot (12 × 12).
What counts as square footage in a house
US property measurement generally follows the ANSI Z765 standard: finished, heated living space measured to the outside of the exterior walls.
- Counted: finished rooms, hallways, stairs and closets with at least 7 ft of ceiling.
- Not counted: garages, unfinished basements, unheated porches and unfinished attics.
- Partly counted: sloped-ceiling rooms, usually only the part above 5 ft.
Because listings measure to the outside of walls, they typically come out 5 to 10% larger than your interior total. For flooring, always use your own interior measurements.
Common mistakes when measuring
- Multiplying before converting inches. Convert each side to feet first.
- Measuring at one point only. Walls are not straight; take the largest of two or three readings.
- Forgetting doorways. Add the strips where flooring runs between rooms.
- Ordering the exact amount. Always add a wastage allowance.
Frequently asked questions
How do I calculate the square footage of a room?
Measure length and width in feet and multiply. A 12 ft × 16 ft room is 192 sq ft. If you measured in inches, divide each by 12 before multiplying.
How do I measure a room that is not a rectangle?
Split it into simple shapes, work out each one and add them. An L-shaped room becomes two rectangles; an angled corner is a triangle (½ × base × height).
How much extra flooring should I order?
About 10% for straight lay, 15% for diagonal or herringbone and 20% for patterned carpet or tile. Add 5% more for rooms with many corners or doorways.
Does square footage include hallways and closets?
For flooring, include every area you will cover. Property listings follow ANSI Z765, which counts finished heated space measured to the outside of exterior walls, so they come out larger.
How many square feet are in a square metre?
About 10.764. A square yard is 9 sq ft and an acre is 43,560 sq ft.
Should I subtract furniture?
No. Flooring runs underneath, so measure the room as if it were empty.
Related tools
Accuracy note: Every area formula, conversion factor and worked example here is re-derived from first principles. Material quantities are guidance only, so confirm with your supplier or installer before ordering.
Content Lead, Anchor AI Tools, California, USA. Spotted an error? Email hello@anchoraitools.com and it will be checked and corrected. See our editorial standards.