How to Calculate Square Footage of a Room, Yard or Irregular Shape
Square footage is the starting point for almost every home project, from flooring and paint to mulch and sod. The math is simple once you know which formula fits the shape. Here are the ones you will use most.
Rectangles and squares
Multiply length by width, both in feet. A 12×15 foot room is 12 × 15 = 180 square feet.
If your measurements include inches, convert them to decimal feet first by dividing the inches by 12. For example, 8 feet 9 inches is 8.75 feet, because 9 ÷ 12 = 0.75.
Formulas for common shapes
| Shape | Formula | Example |
|---|---|---|
| Rectangle | Length × width | 12 × 15 = 180 sq ft |
| Triangle | ½ × base × height | ½ × 10 × 6 = 30 sq ft |
| Circle | 3.14 × radius × radius | 3.14 × 4 × 4 = about 50 sq ft |
For a circle, the radius is half the distance across. An 8-foot wide circle has a radius of 4 feet.
L-shaped and irregular rooms
Split the space into rectangles, find the area of each, and add them. An L-shaped room made from a 12×14 foot section and a 6×8 foot section has 168 + 48 = 216 square feet. If a section is missing a corner or has a bay window, treat it as a rectangle plus a triangle.
Other useful conversions
- Square yards: divide square feet by 9
- Acres: divide square feet by 43,560
- Cubic yards of material: multiply area by depth in feet, then divide by 27
The last one is handy for mulch, gravel and soil. A 100 square foot bed filled 3 inches deep holds 100 × 0.25 = 25 cubic feet, or about 0.93 cubic yards.
When to subtract
For flooring, measure the whole room and subtract only things the floor will not go under, such as a fixed island. For walls, subtract doors and windows. For lawns and beds, subtract patios, trees and anything you won't cover. Our flooring calculator turns your square footage into boxes and cost.
Common mistakes
- Mixing feet and inches in the same multiplication
- Using the diameter instead of the radius for a circle
- Forgetting the ½ in a triangle formula
- Rounding down instead of up when buying materials
For a full walkthrough of measuring and waste allowances, see our guide on measuring a room for flooring, paint and tile.
Enter your room size, waste allowance and price to see how many boxes of flooring you need and what the material costs.
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