The square footage calculator works out the area of a room, a yard, a deck or a patio in square feet. Measure the space in feet, split it into pieces the calculator knows, rectangles, triangles, circles and trapezoids, and it adds the pieces and converts the total to square yards, square meters and acres.
The conversions are the National Institute of Standards and Technology's, from Handbook 44: 9 square feet to the square yard, 43,560 square feet to the acre and exactly 0.09290304 square meter to the square foot.
How to use it
- 01
Measure in feet
Measure each side with a tape or a measuring wheel and enter it in feet. A measurement in feet and inches becomes decimal feet by dividing the inches by 12: 12 feet 6 inches is 12.5 feet, 8 feet 3 inches is 8.25.
- 02
Split the area into simple shapes
An L-shaped room or yard is two rectangles; a yard with an angled corner is a rectangle and a triangle; a round patio is a circle. Draw the space, cut it into pieces that do not overlap, and enter each piece as a section.
- 03
Read the total and convert
The calculator adds the sections. Use square feet for flooring, decking, pavers and sod, square yards for carpet, and acres for a lot.
How the math works
Rectangle and triangle
Rectangle = length × width: a 12 × 10 ft room is 120 sq ft. Triangle = base × height ÷ 2, the height measured square to the base: a corner 12 ft along one side and 10 ft along the other is 60 sq ft.
Circle and trapezoid
Circle = π × diameter² ÷ 4: a 10 ft round patio is 78.5 sq ft. Trapezoid, a piece with two parallel sides, = (side 1 + side 2) ÷ 2 × the height between them: sides of 10 and 14 ft, 8 ft apart, make 96 sq ft.
Converting the total
Square yards = square feet ÷ 9; acres = square feet ÷ 43,560; square meters = square feet × 0.09290304. A 720 sq ft L-shaped yard, 20 × 30 ft plus 10 × 12 ft, is 80 sq yd, 66.9 m² and 0.017 acre.
Worked examples
| Size (ft) | Square feet | Square yards | Square meters |
|---|---|---|---|
| 10 × 10 | 100 | 11.1 | 9.3 |
| 10 × 12 | 120 | 13.3 | 11.1 |
| 12 × 12 | 144 | 16.0 | 13.4 |
| 12 × 16 | 192 | 21.3 | 17.8 |
| 16 × 20 | 320 | 35.6 | 29.7 |
| 20 × 20 | 400 | 44.4 | 37.2 |
| 20 × 30 | 600 | 66.7 | 55.7 |
| 30 × 40 | 1,200 | 133.3 | 111.5 |
Rectangles, length × width; square yards and meters by NIST Handbook 44's units, rounded to one decimal.
Where the number goes wrong
- Entering inches as feet. 6 inches is 0.5 ft, not 6.
- Counting a corner twice. Split an L-shape so the pieces meet along a line and do not overlap.
- Measuring a triangle's slanted side as its height. The height is measured square to the base.
- Using the diameter where the formula wants the radius, or the other way round. The calculator asks for the diameter, the distance straight across.
Questions people ask
How do you calculate square feet?
Multiply the length by the width, both in feet: a 12 × 10 ft room is 120 square feet. For an irregular space, split it into rectangles, triangles and circles, work out each and add them.
How many square feet are in a square yard?
9, because a yard is 3 feet and 3 × 3 is 9. Divide square feet by 9 for square yards.
How many square feet are in an acre?
43,560, by NIST Handbook 44. A lot of 10,890 square feet is a quarter acre.
How do you find the square footage of an L-shaped room or yard?
Cut it into two rectangles that do not overlap, work out each and add them: 20 × 30 ft plus 10 × 12 ft is 600 + 120 = 720 square feet.
How do you convert square feet to square meters?
Multiply by 0.09290304, the exact factor NIST gives: 120 square feet is 11.15 square meters.