How to use the square footage calculator
- Pick the shape: rectangle, triangle or circle.
- Enter the measurements in feet, or switch to metric and use metres.
- If you have several identical areas, such as two matching bedrooms, enter how many.
- Add a price per square foot if you want a cost estimate for flooring, sod or another material priced by area.
The result updates as you type. Use Reset to return to the example values. Most projects on Decoratoradvice start with this measurement, so it is worth taking it carefully.
Square footage formulas
Rectangle or square: area = length × width
Triangle: area = ½ × base × height
Circle: area = π × (diameter ÷ 2)²
The height of a triangle is measured at a right angle to the base, not along the sloping side.
To convert, divide square feet by 9 for square yards, or by 10.764 for square metres.
Worked example
A living room measures 15 ft by 12 ft.
15 ft × 12 ft = 180 sq ft
180 sq ft ÷ 9 = 20 sq yd
If the flooring you like costs $3.50 per square foot, the material for the bare floor area is 180 × $3.50 = $630. Most materials need extra for cutting, so run the area through the flooring calculator to see boxes with waste included.
A round rug 10 ft across covers π × 5² = 78.54 sq ft.
Measuring rooms that are not rectangles
Split the space into simple shapes, find the area of each, then add them together. For an L-shaped room:
| Part | Length | Width | Area |
|---|---|---|---|
| Main room | 15 ft | 12 ft | 180 sq ft |
| Alcove | 6 ft | 4 ft | 24 sq ft |
| Total | 204 sq ft |
For a bay window or angled corner, treat the angled part as a triangle and add it to the rectangle beside it.
Tips for accurate measurements
- Measure at floor level from wall to wall, not along the baseboard, which can hide gaps.
- Convert inches to decimal feet before multiplying: 12 ft 6 in is 12.5 ft, not 12.6 ft.
- Measure each wall of a room that looks square. Older houses are often out by an inch or more.
- Write measurements on a quick sketch so you do not count an area twice.
Common mistakes
- Mixing units. Multiplying feet by inches gives a meaningless number. Convert first.
- Dividing by 3 instead of 9. A square yard is 3 ft × 3 ft, so it holds 9 sq ft.
- Using area for things sold by volume. Gravel, mulch and concrete need depth too; use the cubic yard calculator.
- Using floor area for a roof. A sloped roof has more surface than the floor beneath it. The roofing calculator adds the pitch.
Frequently asked questions
How do I calculate square footage?
Multiply the length by the width, both in feet. For other shapes, use the triangle or circle formula above, or split the space into rectangles and add them.
How many square feet are in a square yard?
Nine. A square yard measures 3 ft on each side, and 3 × 3 = 9.
How do I convert inches to feet for square footage?
Divide the inches by 12 and add them to the feet. 10 ft 9 in is 10 + 9 ÷ 12 = 10.75 ft.
How do I find the square footage of an L-shaped room?
Divide it into two rectangles, find the area of each, and add the results. The table above shows a 180 sq ft room with a 24 sq ft alcove totalling 204 sq ft.
Does square footage for a project include closets?
Include every area you will cover. For flooring that runs into a closet, add the closet floor. For Paint Calculator, you need wall area instead, which the paint calculator works out from the room's dimensions.
How much grass do I need for a lawn?
Measure the lawn's area in square feet, then use the sod calculator to turn that area into pieces and pallets with a small allowance for cuts.
Key takeaways
- Square feet = length × width, with both measurements in feet.
- Divide by 9 for square yards and by 10.764 for square metres.
- Break odd shapes into rectangles, triangles and circles, then add them.
- Area is only the starting point: add waste for flooring and tile, and depth for bulk materials.