How to calculate square footage
For a rectangular room, multiply length × width. A room 12 ft by 14 ft is 168 square feet. For an L-shaped or irregular room, split it into rectangles, calculate each, and add them up — that’s exactly what the list above is for.
| Shape | Formula |
|---|---|
| Rectangle / square | length × width |
| Circle | π × (diameter ÷ 2)² |
| Triangle | base × height ÷ 2 |
| Trapezoid | (side a + side b) ÷ 2 × height |
Measuring tips
- Measure wall to wall at floor level, and round up to the nearest inch.
- Convert inches to feet by dividing by 12 (5′ 6″ = 5.5 ft), or switch the unit to inches.
- Include closets if you’re buying flooring; exclude them for paint or furniture planning.
- For home listings, square footage usually means finished, heated living space — garages, unfinished basements and porches are typically excluded.
How much extra material to buy
Add a waste allowance for cuts and mistakes: about 5–10% for carpet and straight-laid flooring, 10–15% for tile and diagonal or herringbone patterns. Keep a few spare boxes for future repairs — matching batches later can be hard.
Converting square feet
1 square yard = 9 sq ft (carpet is often priced per square yard), 1 square meter ≈ 10.764 sq ft, and 1 acre = 43,560 sq ft. For other area units, use the area converter. For roofs, use the roof pitch calculator, since sloped surfaces have more area than their footprint.
Frequently asked questions
How do I calculate square feet?
Multiply length by width in feet. For irregular spaces, split them into rectangles and add the areas.
How many square feet is a 12×12 room?
144 square feet.
How much extra flooring should I buy?
Usually 5–10% extra, or 10–15% for tile and patterned layouts.
How do I convert square meters to square feet?
Multiply by 10.764. The calculator converts automatically when you choose meters.