Area formula by shape
Square footage is length times width for a rectangle. Other shapes have their own formula, and any real room breaks down into a few of these added together.
| Shape | Area formula | Where it fits |
|---|---|---|
| Rectangle | length × width | Rooms, floors, walls, decks |
| Triangle | ½ × base × height | Gables, corners, angled rooms |
| Circle | π × radius² | Round patios, pools, tanks |
| Trapezoid | ½ × (base₁ + base₂) × height | Sloped roofs, irregular lots |
Break an odd shape into pieces
There is no single formula for an L-shaped or irregular room. Split it into rectangles, triangles and trapezoids, find each area, then add them. For a curved edge, approximate it with a few trapezoids. Always measure wall to wall in feet, and add a 10–15% waste factor when you turn the total into a flooring order.
Feet, metres and common room sizes
- Square feet to square metres. Multiply by 0.0929; reverse by multiplying square metres by 10.76.
- Square feet is not linear feet. Linear feet measure length only; square feet measure area. A board 10 ft long and 2 ft wide is 20 sq ft.
- Rough room sizes. A typical bedroom is 100–150 sq ft, a small kitchen around 70 sq ft, a two-car garage 400–450 sq ft.
Realtor listings can differ from your own measurement: they count finished living space and may leave out garages, basements and porches, or measure to a different wall line.
Common questions
How do I calculate square footage of a room?
For a rectangular room, multiply length by width in feet. A room 12 ft by 10 ft is 120 square feet. Measure wall to wall for a flooring estimate.
How do I find square footage of an L-shaped or odd room?
Split it into rectangles, work out each one, then add them up. A 12x10 section (120 sq ft) plus an 8x6 extension (48 sq ft) is 168 sq ft. Triangles and trapezoids can fill in the corners.
How do I convert square feet to square metres?
Multiply square feet by 0.0929. So 100 sq ft is 9.29 sq m. To go back, multiply square metres by 10.76.
