Quick answer: To find the square footage of an L-shaped or irregular room, split the floor into simple shapes (rectangles, triangles and circles), work out each area, then add them together. An L-shaped room made of a 20 × 8 ft section and a 10 × 12 ft section is 160 + 120 = 280 sq ft. Add 5 to 10% when buying flooring.
The split-and-add method
- Sketch the room and mark every wall length.
- Split it into rectangles, and triangles or part circles for angled or curved walls.
- Measure each piece in feet. Convert inches by dividing by 12: 6 inches is 0.5 ft.
- Calculate each area with the formulas below.
- Add the pieces, and subtract any area you want to exclude, such as a fixed kitchen island or a chimney breast.
L-shaped rooms: two ways
Method 1, add: split into rectangle A (20 × 8 = 160 sq ft) and rectangle B (10 × 12 = 120 sq ft). Total: 280 sq ft.
Method 2, subtract: measure the full outer rectangle (20 × 20 = 400 sq ft) and subtract the missing corner (10 × 12 = 120 sq ft). Total: 280 sq ft. Both methods should agree, which is a good check on your measurements.
Area formulas for odd shapes
| Shape | Formula | Example |
|---|---|---|
| Rectangle or square | length × width | 12 × 14 = 168 sq ft |
| Right triangle (angled wall) | ½ × base × height | ½ × 6 × 4 = 12 sq ft |
| Trapezoid (bay window) | (side a + side b) ÷ 2 × depth | (8 + 4) ÷ 2 × 2 = 12 sq ft |
| Circle | π × radius² | π × 5² = 78.54 sq ft |
| Half circle (curved bay) | π × radius² ÷ 2 | π × 5² ÷ 2 = 39.27 sq ft |
| Quarter circle | π × radius² ÷ 4 | π × 4² ÷ 4 = 12.57 sq ft |
Worked example: a room with a bay window
Living room with a trapezoid bay
- Main room: 16 ft 6 in × 13 ft = 16.5 × 13 = 214.5 sq ft.
- Bay: front 8 ft, back opening 4 ft wide at the glass, depth 2 ft: (8 + 4) ÷ 2 × 2 = 12 sq ft.
- Total floor area: 214.5 + 12 = 226.5 sq ft.
- For flooring with 10% waste: 226.5 × 1.10 = 249.2, so buy 250 sq ft.
Result: 226.5 sq ft, 250 sq ft of flooring
Closets, islands and fixed features
| Feature | Include in floor area? | Why |
|---|---|---|
| Closets | Yes, for flooring | They get the same flooring and need material |
| Fixed kitchen island | No | Flooring usually stops at the cabinet base |
| Chimney breast or column | No | Measure and subtract it |
| Stairs | Measure separately | Treads and risers are priced per step |
| Doorway thresholds | Add a small allowance | Flooring runs to the middle of the door |
How much extra to buy
| Material and layout | Add for waste |
|---|---|
| Carpet, sheet vinyl, simple rooms | 5 to 10% |
| Laminate or vinyl plank, straight lay | 7 to 10% |
| Tile, straight lay | 10% |
| Diagonal tile or plank | 15% |
| Herringbone or chevron | 15 to 20% |
Square feet to square meters
Multiply square feet by 0.092903 to get square meters, or divide square meters by 0.092903 for square feet. 280 sq ft is 26.01 m². The square feet to square meters converter does it both ways.
Measuring tips that avoid mistakes
- Measure at floor level, wall to wall, not at the baseboard top.
- Round each measurement up to the nearest inch, not down.
- Measure twice in different places. Old walls are rarely straight.
- Keep the sketch with every dimension for the store or installer.
- Check the total with the subtract method for L and U shapes.
Frequently asked questions
How do I calculate square footage of an L-shaped room?
Split the L into two rectangles, multiply length by width for each and add them. A 20 × 8 ft section plus a 10 × 12 ft section is 280 sq ft.
How do I find the square footage of an irregular shape?
Break it into rectangles, triangles and circles, calculate each with its own formula, then add them together.
Do closets count in square footage?
For flooring, yes, because they need material. For home listings, closets inside finished living space are usually included too.
How much extra flooring should I buy?
5 to 10% for straight installs and 15% or more for diagonal or herringbone patterns.
How do I measure a room with a bay window?
Measure the main rectangle, then treat the bay as a trapezoid: add the front and back widths, divide by 2 and multiply by the depth.
How do I convert square feet to square meters?
Multiply by 0.092903. 100 sq ft is 9.29 m².
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