Area Formulas
| Shape | Formula | Example |
|---|
| Rectangle | length × width | 12×12 = 144 sq ft |
| Square | side² | 10² = 100 sq ft |
| Circle | π × radius² | r=5 → 78.5 sq ft |
| Triangle | 0.5 × base × height | 10×8 → 40 sq ft |
| Trapezoid | (top+bottom)/2 × height | (6+10)/2×8 = 64 sq ft |
Related: Try our paint calculator, flooring calculator, or concrete calculator for your project.
Conversions
- 1 square foot = 144 square inches
- 1 square yard = 9 square feet
- 1 square meter = 10.764 square feet
- 1 acre = 43,560 square feet
Tip: For irregular rooms, divide into rectangles and calculate each separately. Measure wall-to-wall, not baseboard-to-baseboard.
How to Calculate Square Footage: Step by Step
Whether you are buying flooring, painting walls, ordering concrete, or listing a property, accurate square footage is the foundation of every estimate. Follow these steps to get it right the first time.
- Gather your tools. You will need a tape measure (25 ft or longer), a notepad or phone, a calculator, and optionally a laser distance meter for large rooms. For outdoor areas, a measuring wheel saves time.
- Measure length and width. For rectangular or square rooms, measure the longest two perpendicular walls. Record both dimensions in feet, rounding to the nearest inch. Convert inches to decimals (e.g., 12 ft 6 in = 12.5 ft) before multiplying.
- Multiply length by width. This gives you the gross square footage. For example, a room 14 feet long and 12 feet wide is 14 × 12 = 168 square feet.
- Adjust for obstructions. If you are calculating floor area for material ordering, you generally do not subtract built-in cabinets or fixtures. For wall area (painting, siding), subtract doors and windows — roughly 20 sq ft per door and 15 sq ft per standard window.
- Add waste factor. For flooring, tile, and carpet, add 5–10% extra for cuts and mistakes. For paint, the coverage rate already accounts for normal waste, but always round up to the nearest gallon.
Common Room Sizes at a Glance
| Room Size (ft) | Square Feet | Square Meters | Typical Use |
|---|
| 10 × 10 | 100 | 9.3 | Small bedroom, office |
| 12 × 12 | 144 | 13.4 | Standard bedroom |
| 12 × 16 | 192 | 17.8 | Large bedroom, dining room |
| 14 × 16 | 224 | 20.8 | Master bedroom, living room |
| 16 × 20 | 320 | 29.7 | Large living room, garage |
| 20 × 24 | 480 | 44.6 | Two-car garage, great room |
| 24 × 24 | 576 | 53.5 | Large garage, workshop |
Measuring Odd-Shaped Rooms
Not every room is a perfect rectangle. L-shaped rooms, bay windows, closets, and sloped ceilings require a bit more work. The most reliable method is to divide and conquer: split the space into simple rectangles, calculate each one, then add the results.
For an L-shaped room, draw an imaginary line across the "L" to create two rectangles. Measure each rectangle separately and sum the areas. For rooms with bay windows, measure the main rectangle first, then calculate the bay as a separate rectangle or triangle and add it. For closets, include them if you are measuring total floor area, but exclude them if you are calculating usable living space for real estate listings (local rules vary).
For curved walls, approximate the curve as a series of short straight segments, or use the formula for a circular segment if the curve is a smooth arc. When in doubt, overestimate slightly — it is always cheaper to return unused material than to run out mid-project.
Square Footage for Common Projects
Square footage is the starting point for almost every home improvement material estimate. Here is how it translates to popular projects:
- Flooring: Total sq ft × (1 + waste %) ÷ coverage per box = number of boxes. Hardwood and laminate typically come in boxes covering 18–30 sq ft.
- Paint: Wall sq ft × number of coats ÷ 350 sq ft per gallon = gallons needed. Use our paint calculator for doors, windows, and ceilings.
- Concrete: Sq ft × thickness (in feet) = cubic feet. Divide by 27 for cubic yards. Our concrete calculator handles this automatically.
- Tile: Sq ft × (1 + waste %) ÷ tile area (in sq ft) = number of tiles. Add 10% waste for intricate layouts.
- Roofing: Roof sq ft ÷ 100 = number of "squares." One square of shingles covers 100 sq ft.
Common Mistakes to Avoid
- Forgetting to convert units. Mixing feet and inches is the #1 error. Always convert to decimal feet (6 in = 0.5 ft) before multiplying.
- Measuring baseboard to baseboard. Measure wall to wall for floor area. Baseboards add a small but cumulative error across a whole house.
- Ignoring waste. Ordering exactly the calculated amount guarantees a mid-project store run. Add 5–10%.
- Confusing square feet with linear feet. Trim, molding, and baseboards are sold by the linear foot, not square foot. Measure perimeter for those.
- Rounding down. Always round up to the next whole unit (box, gallon, yard). Partial boxes are rarely sold.
FAQ
How to calculate square footage?
Rectangle: length × width. Circle: π × radius². Triangle: 0.5 × base × height. Always measure in feet.
12×12 room is how many sq ft?
144 square feet.
How to measure irregular rooms?
Divide into rectangles/triangles, calculate each area, then add together.
Sq ft to sq yards?
Divide by 9. 1 square yard = 9 square feet.