How square footage is calculated
Area of a rectangle = length × width
Total area = room 1 + room 2 + …
Square metres = square feet ÷ 10.764 · Square yards = square feet ÷ 9
Measure each room wall to wall at floor level, in feet. If a measurement has inches, divide the inches by 12 and add them to the feet: 12 ft 6 in is 12.5 ft, 9 ft 3 in is 9.25 ft. You can also type the measurement as 12'6" and the calculator converts it for you.
Worked example: two rooms
A bedroom measures 12 ft 6 in by 10 ft, and a living room 14 ft by 11 ft.
- Bedroom: 12.5 × 10 = 125 sq ft
- Living room: 14 × 11 = 154 sq ft
- Total: 125 + 154 = 279 sq ft, which is 25.92 m² or 31 square yards
If the flooring you want costs 3.50 per square foot, the material for 279 sq ft costs 279 × 3.50 = 976.50 before waste. Flooring and tile are bought with an extra allowance for cuts, so use the flooring calculator or tile calculator for the amount to order.
Irregular rooms: split them into rectangles
An L-shaped room is two rectangles. Measure the long side as one rectangle and the leftover leg as a second one, making sure the two do not overlap. A room that is 20 ft by 12 ft with a 8 ft by 6 ft alcove is 240 + 48 = 288 sq ft. Enter each part as its own room in the calculator.
For other shapes, work them out separately and add them to the total:
| Shape | Formula | Example |
|---|---|---|
| Rectangle or square | length × width | 12 × 10 = 120 sq ft |
| Triangle | base × height ÷ 2 | 10 × 6 ÷ 2 = 30 sq ft |
| Circle | π × radius² | 10 ft across: 3.1416 × 5² = 78.54 sq ft |
| Half circle (bay) | π × radius² ÷ 2 | 8 ft across: 3.1416 × 16 ÷ 2 = 25.13 sq ft |
Converting between units
| From | To | Multiply by |
|---|---|---|
| square feet | square metres | 0.092903 |
| square metres | square feet | 10.7639 |
| square feet | square yards | 0.1111 (÷ 9) |
| square yards | square feet | 9 |
| square feet | acres | ÷ 43,560 |
Carpet is often priced per square yard in the US. A price of 27 per square yard is 27 ÷ 9 = 3 per square foot.
Measuring tips
- Measure twice, at floor level. Walls are rarely perfectly square, so measure each room at both ends and use the larger number.
- Include closets and doorways if the flooring runs into them. Leave out areas under kitchen cabinets and bathtubs.
- Round up to the next inch, not down. Being half an inch short on a whole room means a cut piece that does not fit.
- Write measurements on a sketch. A quick floor plan makes it easy to check that rectangles do not overlap.
Floor area is not the same as listed home size
The square footage on a property listing usually measures the outside of the home or follows local measuring standards, so it includes walls and may exclude garages and unfinished basements. In the US, the ANSI Z765 standard is commonly used for single-family homes. For buying materials, always measure the actual rooms rather than relying on the listed size.
Common mistakes
- Adding inches as decimals: 12 ft 6 in is 12.5 ft, not 12.6 ft. The difference over a 10-ft wide room is 1 sq ft.
- Multiplying perimeter instead of length × width. Perimeter (the distance around the room) is what you need for baseboards, not for flooring.
- Mixing feet and metres in one calculation. Pick one unit for every measurement.
Frequently asked questions
How do I calculate square footage?
Multiply the length by the width, both in feet. A room 12 ft 6 in by 10 ft is 12.5 × 10 = 125 sq ft. For several rooms, add the areas together.
How do I convert inches to feet for square footage?
Divide the inches by 12 and add them to the feet: 6 inches is 0.5 ft, so 12 ft 6 in is 12.5 ft. If both sides are in inches, multiply them and divide by 144.
How do I find the square footage of an L-shaped room?
Split it into two rectangles that do not overlap, work out each area and add them. A 20 × 12 ft room with an 8 × 6 ft alcove is 240 + 48 = 288 sq ft.
How many square feet are in a square metre?
One square metre is 10.764 square feet. To go from square feet to square metres, multiply by 0.0929 (or divide by 10.764).
Sources
- National Institute of Standards and Technology (NIST), Handbook 44 Appendix C: units of area (1 ft = 0.3048 m exactly).
- ANSI Z765, Single-Family Residential Buildings – Square Footage Method for Calculating (Home Innovation Research Labs).
Last reviewed 20 October 2026. Results are estimates; see our disclaimer.