How square footage is calculated
Square footage is the floor area of a space in square feet. For a rectangular room it is simply length times width, both measured in feet.
If a measurement includes inches, divide the inches by 12 first. 6 inches is 0.5 ft, 3 inches is 0.25 ft and 9 inches is 0.75 ft. For metric measurements, multiply metres by metres to get square metres, and convert with 1 ft² = 0.09290304 m² (exact, because a foot is exactly 0.3048 m).
The calculator also handles two other shapes that come up in homes and gardens:
For more unusual shapes, such as trapezoids, ellipses or sectors, use the area calculator.
Worked examples
Two rooms of flooring. A living room is 15 ft × 12 ft and a bedroom is 12 ft × 10 ft 6 in. You want laminate at $3.50 per sq ft with 10% waste.
- Living room: 15 × 12 = 180 sq ft.
- Bedroom: 12 × 10.5 = 126 sq ft.
- Total: 180 + 126 = 306 sq ft (28.43 m²).
- With 10% waste: 306 × 1.10 = 336.6 sq ft to buy.
- Cost: 336.6 × $3.50 = $1,178.10.
An L-shaped room. The room is 20 ft along the long wall and 14 ft along the short one, with a 8 ft × 6 ft corner cut out by a staircase. Split it into two rectangles that do not overlap: 20 × 8 = 160 sq ft and 12 × 6 = 72 sq ft. The total is 232 sq ft. (You can check it another way: 20 × 14 = 280, minus the 8 × 6 = 48 corner, also gives 232.)
A metric tiling job. A bathroom floor is 2.4 m × 1.8 m. The area is 2.4 × 1.8 = 4.32 m² (46.5 sq ft). Tiles are laid on the diagonal, so allow 15%: 4.32 × 1.15 = 4.97 m², so buy 5 m² of tiles.
Common room sizes
| Room size | Square feet | Square metres | Square yards |
|---|---|---|---|
| 10 × 10 ft | 100 | 9.29 | 11.1 |
| 10 × 12 ft | 120 | 11.15 | 13.3 |
| 12 × 12 ft | 144 | 13.38 | 16.0 |
| 12 × 15 ft | 180 | 16.72 | 20.0 |
| 14 × 16 ft | 224 | 20.81 | 24.9 |
| 15 × 20 ft | 300 | 27.87 | 33.3 |
| 20 × 20 ft | 400 | 37.16 | 44.4 |
Carpet in the US is sometimes priced per square yard. One square yard is 9 square feet, so divide square feet by 9.
How much waste to allow
Every flooring job loses some material to cuts at walls, doorways and around obstacles. Common allowances are:
| Job | Typical waste |
|---|---|
| Carpet, sheet vinyl, straight-laid laminate or plank | 5–10% |
| Tiles in a straight grid | 10% |
| Diagonal tiles, herringbone or chevron | 15–20% |
| Small rooms with many corners | Add 5% to the above |
These are rules of thumb. The flooring maker’s installation guide is the best source for a particular product. Buying a box or two extra also gives you spares from the same batch for future repairs.
Measuring tips
- Measure wall to wall at floor level, and measure each room at its widest points.
- Round up to the next inch when buying materials. Round down only when you are working out the usable area of a space you are buying or renting.
- Measure walls twice. Older rooms are often slightly out of square. Use the longer measurement.
- Include closets and alcoves if the flooring goes into them. Leave out areas under fitted kitchen units if the floor will not run underneath.
- Use quantity for repeats. Three identical bedrooms can be one row with a quantity of 3.
Square footage for a house
When a home is listed for sale, the square footage normally means the finished, heated living area, measured from the outside of the walls. Garages, unfinished basements and open porches are usually listed separately. The exact rules differ by country and by lender, so this calculator is best used for materials and planning rather than legal or valuation figures.
Next steps
Once you know the area, you can go further. The concrete calculator turns a slab’s area and thickness into cubic yards and bags, and the roofing calculator adds pitch to a footprint to find roof squares and shingle bundles. To change one length from metres to feet, use the length converter.