How square footage is calculated
Turn each measurement into feet (feet + inches ÷ 12), find the area of each section, then add the sections and subtract any cutouts.
Total sq ft = sum of added sections − sum of subtracted sections
| Shape | Area |
|---|---|
| Rectangle or square | length × width |
| L-shape | part 1 length × width + part 2 length × width |
| Circle | π × (diameter ÷ 2)² |
| Half circle | π × (diameter ÷ 2)² ÷ 2 |
| Triangle | ½ × base × height |
| Trapezoid | (side a + side b) ÷ 2 × height |
With waste = total × (1 + waste % ÷ 100) · Cost = sq ft with waste × price per sq ft
Worked example
A living room is 15 ft 6 in by 12 ft: 15.5 × 12 = 186 sq ft. Its closet is 4 ft by 3 ft 6 in: 4 × 3.5 = 14 sq ft. A built-in cabinet you won't floor under is 3 ft by 2 ft, so subtract 6 sq ft. Total: 186 + 14 − 6 = 194 sq ft, which is 21.56 sq yd or 18.02 m². With 10% extra for cuts that's 213.4 sq ft, and at $3.25 per sq ft about $693.55.
Measuring an L-shaped or odd room
- Split the floor into rectangles that don't overlap. For an L, draw one line across where the two legs meet.
- Measure to the wall, not the baseboard, and round each measurement up to the next inch.
- A bay window bump-out is usually a trapezoid, and a rounded bump-out is often a half circle.
- Use Subtract for things the floor doesn't run under, like a kitchen island, a fireplace hearth or a bathtub.
Units and conversions
1 square yard is 9 sq ft (3 ft × 3 ft). Carpet is often priced per square yard. 1 sq ft is 0.09290304 m² exactly, because 1 ft is 0.3048 m. An acre is 43,560 sq ft.
Limitations
- House size in a listing follows its own rules (like ANSI Z765), which count finished, heated space and exclude garages. This page just adds the areas you enter.
- Waste depends on the material and layout: allow about 5–10% for straight layouts, 10–15% for diagonal or patterned layouts. Flooring is sold in whole boxes, so use the flooring calculator for box counts.
- Walls and ceilings aren't included. For paint, use the paint calculator.
Sources
- NIST Guide to the SI, Appendix B.8 (exact conversion factors: 1 ft = 0.3048 m, 1 ft² = 0.09290304 m²; Calcist uses the international acre of 43,560 sq ft = 4,046.8564224 m²)