How to use the square footage calculator
- Sketch the space. On paper, draw the outline of the room, yard or roof section and split it into rectangles, triangles, circles or trapezoids.
- Measure each part in feet (or switch to metric). Inches are fine too: type 12' 6" or 12.5.
- Add a row for each part. Tick Subtract this for anything you do not want counted, such as a fireplace hearth, a stair opening or a pond.
- Send the total on. Use the buttons under the result to carry the area into the gravel or asphalt calculator.
Area formulas
Rectangle = length × width
Triangle = base × height ÷ 2
Circle = π × radius², where radius = diameter ÷ 2
Trapezoid = (side A + side B) ÷ 2 × height
For a triangle, the height is measured square to the base, not along a sloping side. For a trapezoid, sides A and B are the two parallel sides.
Worked example
A 12 × 15 ft room with a triangular bay
- Main room: 12 × 15 = 180 sq ft.
- Bay: base 6 ft, height 4 ft, so 6 × 4 ÷ 2 = 12 sq ft.
- Total = 180 + 12 = 192 sq ft, or 21.3 square yards.
Measuring tips
- Measure wall to wall at floor level, and measure twice. Rooms are rarely perfectly square, so measure both ends and use the larger figure.
- Round up to the next inch, not down.
- For curved edges, such as a garden bed, treat the curve as a few short straight parts, or use the circle that fits it best. For a half circle, work out the full circle and halve it.
- For a sloped yard, measure horizontally if you are buying by area for a flat product; measure along the slope if you are covering the slope itself.
Unit conversions
| From | To | Multiply by |
|---|---|---|
| Square feet | Square yards | ÷ 9 |
| Square feet | Square metres | × 0.0929 |
| Square metres | Square feet | × 10.764 |
| Square inches | Square feet | ÷ 144 |
| Square feet | Acres | ÷ 43,560 |
Common mistakes to avoid
- Counting overlaps twice. When you split an L-shape, make sure the two rectangles do not share any floor.
- Using a sloping side as the triangle height. Height is the straight distance from the base to the tip.
- Dividing square feet by 3 to get square yards. It is 9, not 3.
- Buying the exact area. For anything that is cut to fit, add 5 to 15% under Adjust assumptions.
Frequently asked questions
How do I calculate square footage?
Measure the length and width in feet and multiply them. A room 12 ft by 15 ft is 180 square feet. For odd shapes, split the space into rectangles and triangles, work out each one and add them together.
How do I find the square footage of an L-shaped room?
Split the L into two rectangles that do not overlap, work out the area of each and add them. For example, a 20 × 10 ft section plus an 8 × 6 ft section is 200 + 48 = 248 sq ft.
How do I convert inches to square feet?
Multiply length × width in inches and divide by 144, because a square foot is 12 × 12 = 144 square inches. Or switch the unit menu and the calculator converts for you.
How many square feet are in a square yard?
Nine. A yard is 3 feet, so a square yard is 3 × 3 feet. Divide square feet by 9 to get square yards.
Is square footage the same as linear feet?
No. Square feet measure area (length × width). Linear feet measure length only, such as for trim, edging or fencing. The perimeter shown here is in linear feet.
How many square feet are in an acre?
43,560 square feet. A quarter acre is 10,890 sq ft.