How the Square Footage Calculator Works
The area of a space tells you how much surface it covers. It is the number that you need to buy flooring, carpet, tile or paint, to compare homes, or to describe a plot of land. In the United States, area is usually given in square feet. The Square Footage Calculator finds the area of a room or a plot from its measurements, and gives it in every common unit.
What you enter
- The unit of your measurements: feet, inches, yards, meters or centimeters.
- The shape: a rectangle or square, a triangle, a circle or a trapezoid.
- The measurements of the shape. The boxes change with the shape.
- More areas (optional): for a room that is not a simple shape. You can add an area, or take one away.
The formulas
| Shape | You measure | Area |
|---|---|---|
| Rectangle or square | length, width | length x width |
| Triangle | base, height | base x height / 2 |
| Circle | diameter | pi x (diameter / 2) x (diameter / 2) |
| Trapezoid | two parallel sides, and the height between them | (side 1 + side 2) / 2 x height |
- Shape: Rectangle or square
You measure: length, width
Area: length x width - Shape: Triangle
You measure: base, height
Area: base x height / 2 - Shape: Circle
You measure: diameter
Area: pi x (diameter / 2) x (diameter / 2) - Shape: Trapezoid
You measure: two parallel sides, and the height between them
Area: (side 1 + side 2) / 2 x height
All the measurements are changed into feet first, so the area is worked out in square feet. From there the calculator converts it to the other units.
A worked example
A room is 12 feet long and 15 feet wide.
| Unit | Area |
|---|---|
| Square feet (12 x 15) | 180 sq ft |
| Square yards (180 / 9) | 20 sq yd |
| Square meters (180 / 10.7639) | 16.72 m² |
| Square inches (180 x 144) | 25,920 sq in |
| Acres (180 / 43,560) | 0.00413 acres |
Converting between units
| 1 square foot is | 1 square meter is | Other |
|---|---|---|
| 144 square inches | 10.7639 square feet | 1 square yard = 9 square feet |
| 0.1111 square yards | 1.196 square yards | 1 acre = 43,560 square feet |
| 0.092903 square meters | 10,000 square centimeters | 1 acre = 4,046.86 square meters |
- 1 square foot is: 144 square inches
1 square meter is: 10.7639 square feet
Other: 1 square yard = 9 square feet - 1 square foot is: 0.1111 square yards
1 square meter is: 1.196 square yards
Other: 1 acre = 43,560 square feet - 1 square foot is: 0.092903 square meters
1 square meter is: 10,000 square centimeters
Other: 1 acre = 4,046.86 square meters
A common mistake is to convert feet to meters by 3.28, and then to use the same number for area. Area is length times length, so the factor is squared: 3.28 x 3.28 = 10.76. This is why 12 square meters is about 129 square feet, not 39.
Other shapes
The same calculator handles other shapes:
| Shape | Measurements | Area |
|---|---|---|
| Rectangle | 12 ft by 15 ft | 180 sq ft |
| Circle | diameter 10 ft | 78.54 sq ft |
| Trapezoid | sides 8 ft and 12 ft, height 5 ft | 50 sq ft |
| Triangle | base 10 ft, height 6 ft | 30 sq ft |
- Shape: Rectangle
Measurements: 12 ft by 15 ft
Area: 180 sq ft - Shape: Circle
Measurements: diameter 10 ft
Area: 78.54 sq ft - Shape: Trapezoid
Measurements: sides 8 ft and 12 ft, height 5 ft
Area: 50 sq ft - Shape: Triangle
Measurements: base 10 ft, height 6 ft
Area: 30 sq ft
Rectangle ████████████████████████████████████████ 180 sq ft Circle █████████████████ 78.5 sq ft Trapezoid ███████████ 50 sq ft Triangle ███████ 30 sq ft
Rooms with more than one part
Many rooms are not a simple rectangle. To find the area of an L-shaped room, split it into rectangles, work out each one, and add them. If a part is not included, such as a closet, or a stair opening, take it away. For example:
| Part | Measurements | Area |
|---|---|---|
| Main room (add) | 20 ft by 12 ft | 240 sq ft |
| Extension (add) | 8 ft by 6 ft | 48 sq ft |
| Closet (subtract) | 4 ft by 3 ft | -12 sq ft |
| Total | 276 sq ft |
Main room ███████████████████████████████████ 240 Extension ███████ 48 Closet ██ -12 Total ████████████████████████████████████████ 276
Green bars are added, red bars are taken away, and the blue bar is the total. The calculator draws the same chart for your own areas.
Metric measurements
If you measure in meters, the calculator changes them into feet, and shows the area in both systems. A room of 4 m by 3 m is 12 square meters, which is 129.17 square feet. Measurements in centimeters or inches work in the same way: 400 cm by 300 cm is also 129.17 square feet, and 120 inches by 96 inches is exactly 80 square feet.
Some common sizes
For an idea of the size of an area. These are typical examples, and real rooms vary:
Bathroom, 5 x 8 ft ████ 40 sq ft Bedroom, 12 x 12 ft ██████████████ 144 sq ft Living room, 15 x 20 ft ██████████████████████████████ 300 sq ft Two-car garage, 20 x 20 ft ████████████████████████████████████████ 400 sq ft
Uses
- Flooring, carpet and tile. Work out the area, and add some extra for cuts and waste. Carpet is often sold by the square yard.
- Paint. The area of the walls is the length around the room times the height, minus doors and windows. The floor area is only a rough guide.
- Real estate. Homes are compared by their square footage. Different countries, agents and standards measure it in different ways, so compare like with like.
- Land. Plots are often given in acres. 1 acre is 43,560 square feet.
Tips
- Measure twice, to the nearest inch, and write the numbers down.
- Use the same unit for every measurement in one shape.
- Split odd shapes into a rectangle, a triangle or a circle, and add them.
- Include the tiles or boards you will cut off. Buy 5% to 10% extra, and more for patterns.
What this calculator does not include
- Curved shapes other than a circle, such as an oval or a half circle. Split them into parts, or use a full circle and take away the part you do not need.
- Surface area of walls, roofs or objects that are not flat.
- The official way to measure a home for sale, which depends on where you live.
This tool gives an estimate for general information only. Measure carefully, and check important amounts before you buy.